How to Select Inner Layers for Custom Coffee Bags | Freshness Retention, Aroma Protection, Durability

Pure aluminum foil (AL) is the top choice, with oxygen and water vapor transmission rates close to 0, blocking 99.9% of light and moisture, extending coffee bean freshness to 12-18 months, perfectly locking in oils and aroma.

The innermost food-grade PE film ensures 100% food contact safety (BPA-free) and provides excellent heat sealing strength and tear resistance to prevent bag burst.

Freshness Retention

Roasted coffee beans release carbon dioxide and are prone to oxidation.

According to data from the Specialty Coffee Association (SCA), when the oxygen concentration inside the packaging exceeds 1%, the rate of flavor deterioration significantly increases.

The inner film material needs to control the oxygen transmission rate (OTR) below 0.1 cc/m²/24h, combined with a one-way degassing valve to release internal gases.

Controlling Oxygen Rate

After coffee beans are roasted, the aromatic oils within the cell walls rapidly migrate to the surface.

Test data from the U.S. Department of Agriculture (USDA) indicates that the oxidation rate of volatile lipids in dark roasted coffee beans exposed to ambient air for 24 hours increases by 40%.

The industry uniformly uses Oxygen Transmission Rate (OTR) to quantify the barrier level of packaging materials.

According to the ASTM D3985 international testing standard, material measurements are conducted at 23°C and 0% Relative Humidity (RH).

Unit values are calculated in cubic centimeters per square meter per 24 hours (cc/m²/24h).

OTR readings below 0.1 cc/m²/24h meet the storage requirements for North American warehouse supermarkets for up to one year.

When testing the oxygen permeability of inner materials, third-party laboratories use several measurement parameters:

• Test sample area: Uniformly specified as a flat film of 50 square centimeters.
• Permeation gas purity: Single-sided pressure applied using 99.9% pure oxygen.
• Continuous permeation time: Instrument continuously monitors for 48 to 72 hours, then takes the average value.
• Coulometric sensor accuracy: Detects trace oxygen penetration as low as 0.005 cc.

Pure aluminum foil (AL) is the most extreme soft packaging inner film in terms of oxygen barrier performance.

A pure aluminum layer with a thickness of 7 to 9 micrometers, when free from physical damage, has OTR test data infinitely approaching 0.

Large chain supermarkets in North America generally use a PET and aluminum foil composite structure for commercial blend beans.

Metallic aluminum has excellent ductility, and when rolled into foil, it forms a dense metallic crystal arrangement.

The intermolecular spacing is much smaller than the kinetic diameter of oxygen molecules (0.346 nanometers), cutting off the gas diffusion path.

During a 12-month shelf life, the oxygen concentration inside the bag remains at the level of initial sealing.

Metallized polyester film (VMPET) is manufactured using physical vapor deposition (PVD) technology.

In highly vacuumed production equipment, high-purity aluminum wire is heated to vaporize above 1200°C.

Gaseous aluminum atoms adhere to the surface of a 12-micrometer thick PET film, forming a metallic coating.

The thickness of the metallized layer is usually between 400 to 500 Angstroms (Å), less than one ten-thousandth of the diameter of a human hair.

The OTR of VMPET material is controlled within the range of 0.5 to 2.0 cc/m²/24h.

This meets the demand for blocking oxygen penetration for medium roasted single-origin beans within 3 to 6 months.

Coffee beans of different roast levels have different outgassing rates and surface oil adhesion, leading to variations in the tolerable OTR threshold:

• Very light roast (Cinnamon Roast): OTR upper limit relaxed to 2.5 cc/m²/24h.
• Medium roast (City Roast): OTR needs to be below 1.0 cc/m²/24h.
• Dark roast (French Roast): OTR is strictly limited to within 0.1 cc/m²/24h.
• Commercial Espresso Blend: Requires nitrogen filling equipment, OTR value demands close to 0.

Ethylene-vinyl alcohol copolymer (EVOH) is gradually replacing aluminum-containing films as a single recyclable inner layer in the European market.

The molar ratio of ethylene in EVOH resin raw material is usually between 32% to 44%.

The lower the ethylene content, the higher the crystallinity of the polymer, and the stronger its ability to block oxygen.

A 15-micrometer thick EVOH co-extruded film actually achieves an OTR of 0.1 to 0.5 cc/m²/24h.

The EVOH molecular chain contains a large number of hydroxyl (-OH) groups, and the intermolecular hydrogen bonding makes the polymer chains very tightly arranged.

Combined with a nitrogen flushing packaging system (MAP), the barrier data of the inner film plays its role.

Before heat sealing, the sealing equipment on the production line injects 99.9% pure liquid nitrogen into the coffee bag.

This forces the initial residual oxygen in the bag to drop below 2%.

Tests by the Specialty Coffee Association of Europe (SCAE) indicate that for every 1% increase in residual oxygen in the packaging bag, the deterioration period of coffee lipids is shortened by 10%.

If the OTR reading of the inner material is high, free oxygen in the environment, driven by the concentration difference, slowly penetrates into the low-oxygen packaging interior.

The Arrhenius physical equation shows that for every 10°C increase in ambient temperature, the OTR value of polymeric film materials doubles.

During the processing in the bag making workshop, the physical oxygen barrier performance of the inner material is slightly affected by mechanical actions.

The following equipment process parameters lead to an overall OTR of the final product that is higher than the raw material laboratory data:

• Heat seal edge pressure: Excessive pressure causes the inner polyethylene to melt and thin, increasing local oxygen permeability by about 5%.
• Physical bending and friction: The aluminum foil layer develops tiny pinholes due to mechanical folding, and oxygen permeability increases accordingly.
• Degassing valve hot melt point: The welding gap tolerance between the valve base and the film must not exceed 0.02 millimeters.
• Composite adhesive coating: Trace solvent residue in the adhesive interferes with the molecular arrangement stability of the film barrier layer.

The one-way degassing valve has a rubber diaphragm coated with silicone oil embedded inside.

When the carbon dioxide pressure released by the coffee beans inside the bag exceeds 0.5 psi, the diaphragm is pushed open to vent gas.

When external atmospheric pressure drops, the surface tension of the silicone oil quickly reseals the diaphragm against the inner layer.

A hot cutting tool punches a 2-millimeter diameter vent hole in the inner material.

The puncture resistance and tensile strength of the inner film reach over 15 Newtons (N) to prevent microscopic tearing around the hole and eliminate oxygen backflow.

Blocking Moisture Permeation

Freshly roasted coffee beans have a strictly controlled very low moisture content of 1.5% to 2.5%.

Once exposed to an environment with relative humidity (RH) exceeding 60%, the porous fiber structure rapidly adsorbs free water molecules from the air.

The industry uses Water Vapor Transmission Rate (WVTR) to quantify the moisture barrier level.

According to the ASTM F1249 standard, testing is performed under extreme conditions of 37.8°C and 100% relative humidity.

The unit of WVTR measurement is grams per square meter per 24 hours (g/m²/24h).

When the moisture content of coffee beans inside the bag exceeds the critical point of 3.0%, the physical brittleness decreases significantly, leading to a large amount of fines during grinding, which increases the incidence of channeling during espresso extraction by 40%.

Water vapor intrusion accelerates the hydrolysis of surface polyunsaturated fatty acids. For an inner film to maintain an 8-month shelf life in North American supermarkets, its WVTR must be below 0.5 g/m²/24h.

Pure aluminum foil (AL) provides an extremely high level of physical moisture barrier.

An aluminum layer with a thickness of 7 to 9 micrometers, with its dense metallic lattice structure, completely cuts off the penetration path of water vapor molecules.

Under ideal conditions without mechanical damage, the WVTR test data for pure aluminum foil is 0 g/m²/24h.

Condensation in international shipping containers often causes local humidity to soar above 95%, and aluminum foil ensures the dryness of green beans exported from South America to Europe after roasting.

Metallized polyester film (VMPET) has an aluminum atom layer of 400 Angstroms deposited by vapor phase on a 12-micrometer thick PET substrate.

Its WVTR value is usually maintained within the range of 0.5 to 1.5 g/m²/24h.

For regional chain brands with a consumption cycle of within 3 months, VMPET balances physical water resistance and production budget.

The tensile strength of the PET substrate, which is up to 150 MPa, compensates for the physical defect of pure aluminum being extremely prone to creasing and pinholes.

Polyethylene (PE) is often used as the innermost heat-sealable layer in composite packaging and inherently possesses basic hydrophobic properties.

A linear low-density polyethylene with a thickness of 50 to 70 micrometers has a WVTR reading between 5.0 and 8.0 g/m²/24h.

Low-density polyethylene lacks polar groups in its molecular chain, making it extremely difficult for water molecules to dissolve and diffuse on its surface.

Bulk beans sold by roasteries for short-term consumption typically use single-layer PE bags with a thickness exceeding 100 micrometers.

Ethylene-vinyl alcohol copolymer (EVOH) contains a large number of hydroxyl groups in its molecular chain, making it extremely sensitive to moisture.

When the ambient relative humidity exceeds 75%, EVOH absorbs free water from the air, causing its original barrier performance to drop sharply.

When designing single recyclable coffee bags, the co-extrusion process sandwiches a 15-micrometer thick EVOH layer between two polyolefin layers.

An external 60-micrometer PE water barrier layer increases the water vapor blocking rate to the central EVOH layer by up to 98%.

Storage conditions in different climate zones have strict data divisions for the WVTR tolerance of inner films.

Third-party laboratories measure the water barrier degradation performance of different composite materials when simulating equatorial oceanic climate (38°C, 90% RH) and temperate continental climate (20°C, 50% RH).

The data collection period is uniformly set at 120 days.

The thermodynamic processing during the high-speed bag making process of 120 bags/minute in the packaging factory can alter the local microstructure of the film, resulting in actual moisture barrier data for finished coffee bags that are lower than the roll film raw material.

Small fluctuations in physical parameters will increase the overall WVTR test value, and third-party quality inspection will individually check the 5 mechanical stress deformation zones on the production line.

• Heat sealing temperature deviation: Sealing knife temperature exceeding 160°C leads to excessive melting and thinning of the PE layer.
• Tension control malfunction: Winding tension greater than 25N causes micro-cracks in the VMPET coating.
• Adhesive curing residue: Polyurethane adhesive incomplete cross-linking reaction in a 45°C curing room.
• Mechanical corner damage: Water vapor permeability in the bottom folded area of flat bottom bags is 3 times higher than the flat surface.
• Degassing valve back pressure: Uneven cutting edges cause the silicone ring at the valve base to have less than 99% fit.

The zipper embedded 15 millimeters inside the bag opening must have a biting tolerance of less than 0.05 millimeters.

Tests by the North American Specialty Coffee Association show that an incompletely pressed zipper seam will equalize the humidity inside the bag with the external environment within 12 hours.

The 3-millimeter wide extruded moisture-proof strips on both sides of the zipper track reduce the backflow rate of water vapor after opening by 60%.

Coffee beans stored in a household refrigerator at 4°C will instantly condense a large amount of water droplets on the surface of the packaging bag when taken out and placed on a 22°C room temperature table.

The inner film now withstands the reverse permeation pressure of condensation water caused by the sudden drop in temperature.

A 12-micrometer thick biaxially oriented polyester composite with an aluminum coating can resist a 0.2 atm micro pressure difference caused by hot and cold alternation, preventing surface condensation water from permeating into the bag in molecular form and damaging the dryness of the coffee beans.

Blocking UV Rays

Roasted coffee beans have a large amount of unsaturated fatty acids on their surface, which undergo photo-oxidative reactions when exposed to light.

U.S. Department of Agriculture (USDA) tests indicate that ultraviolet (UV) light with wavelengths between 300 to 400 nanometers breaks lipid molecular chains.

Transparent packaging bags exposed to standard 750 lux (lux) cold light in supermarkets for 14 days show a 300% surge in the peroxide value (POV) of the coffee beans inside.

Riboflavin (Vitamin B2) in coffee beans acts as a photosensitizer under light, catalyzing chemical reactions after absorbing photon energy.

When 380-nanometer UV-A light penetrates the packaging film, riboflavin combines with sulfur-containing amino acids to produce 3-methyl-2-buten-1-thiol.

The human sense of smell can detect the “sunlight odor” emitted by this substance at extremely low concentrations of 10 ppt (parts per trillion).

North American third-party laboratories use a UV-Vis spectrophotometer to continuously scan packaging films across a full spectrum from 200 to 800 nanometers.

The industry uniformly uses Optical Density (OD) to quantify the light blocking capability of materials.

Absorbance data has a logarithmic relationship with light transmittance; higher OD readings indicate a thicker physical barrier against light penetration.

Pure aluminum foil (AL) with a thickness set at 7 micrometers provides an absolute physical block with an OD value greater than 4.0.

The extremely flat metallic crystal surface reflects 99.99% of incident photons back into the air, with the remaining minimal photons converted into thermal energy and dissipated within the metal layer.

In a 12-month shelf life simulation test, the light intensity inside the pure aluminum foil bag remained at 0 lux.

The light blocking rate of metallized polyester film (VMPET) is determined by the thickness of the metal atoms attached to its surface.

VMPET selected by North American commercial roasters has an aluminum atom layer thickness controlled at around 400 Angstroms (Å).

Laboratory spectrophotometers measure its OD value to fall within the 2.0 to 2.5 range.

Overall light transmittance is strictly suppressed between 1% and 0.3%.

Ethylene-vinyl alcohol copolymer (EVOH) and polyethylene (PE) in single recyclable materials, as polymeric resins, are inherently highly transparent to visible light.

Chemical factories incorporate 0.1% to 0.5% benzophenone-type UV absorbers into PE masterbatches with a thickness of 60 micrometers to compensate for the poor light blocking of transparent polymer materials.

Polyethylene inner layer doped with 0.3% concentration of UV absorber boosts the blocking rate of UV-B in the 280 to 340 nanometer range to 95%. Absorber molecules capture high-energy UV photons, causing intramolecular proton transfer, converting destructive light energy into low-frequency thermal energy released to the outside of the packaging.

Kraft paper bags with visible windows (Window Bags) are widely used in specialty coffee shops in Europe and America.

A transparent window with an area of 15 square centimeters breaks the original dark room environment of the composite material.

Light rays refract into the inner cavity of the bag, and after accumulating 50,000 lux-hours of irradiation, the Agtron color value of the surface coffee beans shows significant deterioration and fading.

Packaging film engineers enhance the light-blocking performance in the transparent window area by adding multiple co-extrusion coating processes.

The film production line needs to precisely control the following physical processing parameters on the coating unit:

• Coating roller pressure: Maintained at 0.4 MPa to ensure uniform UV coating thickness.
• Drying tunnel temperature: Heated to 120°C to stabilize nano-sized TiO₂ particles for cross-linking.
• Coating dry weight: Transparent barrier coating layer weight reaches 2.5 g/m².
• Haze increment: The overall haze increase of the processed film does not exceed 3%.
• Adhesion peel strength: Interlayer peel strength greater than 1.5 N/15mm to prevent delamination.

The matte varnish on the outermost film surface cooperates with the inner material to synergistically weaken photon penetration.

An anilox roller prints a matte coating approximately 3 micrometers thick on the outer PET layer, reducing surface gloss to below 15 GU (Gloss Units).

The diffuse reflection effect scatters the vertical light beams of supermarket LED spotlights, reducing the unit area pressure of direct light on the inner film.

The coverage rate of surface printed ink pigments also changes the overall test data. Opaque dark black or metallic spot color inks with 100% coverage, combined with the inner EVOH transparent barrier layer, collectively increase the OD value from the original 0.1 to 1.2, physically filtering out 85% of visible light.

The four side seals of flat bottom (Flat Bottom) folded bags have light leakage points.

The 5 to 8 millimeter wide heat-sealed edge, squeezed by high-temperature molds, causes the inner PE layer to thin and lose some of its coating.

Photons pass through the transparent resin gaps at the heat seal indentation, forming a fiber optic effect, refracting along the internal cross-section of the polymer into the coffee bean bed.

Display standards for large European supermarket chains mandate that the distance between the top shelf of coffee and LED light sources be at least 1.2 meters.

Doubling the light source distance reduces the light intensity reaching the packaging surface to one-quarter, according to the inverse square law.

Aroma Protection

Roasted coffee beans produce over 1000 volatile aromatic compounds (VOCs). Without sealing, 40% of these VOCs are lost within 72 hours.

Aroma protection involves establishing a physical gas barrier. This requires the inner layer of the packaging to have an Oxygen Transmission Rate (OTR) below 1.0 cc/m²/day and a Water Vapor Transmission Rate (WVTR) below 1.0 g/m²/day.

Maintaining an internal carbon dioxide concentration of 15%-20% and completely isolating external air can slow down the escape of aromatic molecules like pyrazines and furans, extending the product’s shelf life to 6-12 months.

Material Permeability

ASTM D3985 and F1249 standards, developed by the American Society for Testing and Materials (ASTM), are industrial standards for measuring gas permeability of packaging films.

Laboratories typically test Oxygen Transmission Rate (OTR) at 23°C (73.4°F) and 0% relative humidity (RH), and Water Vapor Transmission Rate (WVTR) at 38°C (100.4°F) and 90% RH.

The physical barrier properties of pure aluminum foil (AL) show a strong positive correlation with thickness variables.

When the aluminum foil thickness reaches 7 micrometers (µm), the number of microscopic pinholes per square meter is usually less than 50, and both OTR and WVTR are stable at extremely low values of 0.01 cc/m²/day and 0.01 g/m²/day.

When the thickness is reduced to 5 micrometers, the number of pinholes will increase exponentially to over 400, and oxygen barrier performance will drop sharply.

The metal layer lacks physical elasticity, and folding or physical compression can damage its microscopic crystal structure.

In the ASTM F392 Gelbo flex test, after 20 standard flex cycles, a 7-micrometer aluminum foil develops tiny physical cracks on its surface, causing the OTR value to instantly rebound from 0.01 to over 1.5 cc/m²/day.

Metallized film (VMPET) is produced by vaporizing solid aluminum wire at 1500°C in a high vacuum environment and depositing it on a 12-micrometer polyester (PET) substrate.

The thickness of the attached metallic aluminum layer is extremely thin, usually measured in Angstroms (Å), with standard industrial specifications for metallized layer thickness maintained between 400 and 500 Angstroms.

The conventional OTR of VMPET is maintained within the range of 0.5 to 1.5 cc/m²/day.

For VMPET used in coffee bags, its OD value must be 2.0 or higher, with some high-oxygen barrier models having an OD value set at 2.5 to 2.8.

For every 0.1 increase in optical density, the film’s blocking rate for visible light between 400 and 700 nanometers and ultraviolet light increases by approximately 3%.

• AL 7µm: Puncture force > 10 N, OTR < 0.01
• AL 9µm: Puncture force > 15 N, puncture resistance improved by 40%
• VMPET 12µm: OD > 2.0, gloss > 110%
• VMPET 15µm: OD > 2.5, tensile strength > 150 MPa

Co-extruded ethylene-vinyl alcohol copolymer (EVOH) provides high-strength gas barrier through hydroxyl groups in its polymer chain.

In environments below 65% relative humidity (RH), a 15-micrometer EVOH film exhibits excellent OTR performance of 0.1 to 0.5 cc/m²/day.

The special polymer structure gives it excellent physical flexibility, maintaining its original oxygen barrier level even after 100 mechanical flexes in Gelbo tests.

When the storage environment’s relative humidity exceeds 80%, EVOH absorbs free water from the air, causing its OTR value to increase logarithmically, potentially soaring up to 5.0 cc/m²/day.

EVOH is combined with polyethylene (PE) or polypropylene (PP) in specific multi-layer composites, with the PE or PP layer acting as a water barrier on the outermost side.

In the classic 5-layer symmetric structure (PE/Tie/EVOH/Tie/PE), the thickness of the EVOH resin layer sandwiched in the middle is precisely controlled between 3 to 5 micrometers, which can stabilize the overall WVTR within 1.5 g/m²/day even in 90% high humidity environments.

Aluminum oxide (ALOx) and silicon oxide (SiOx) coated films provide an alternative physical barrier solution for transparent packaging.

A 10 to 20 nanometer thick inorganic oxide coating is applied to a 12-micrometer PET surface using plasma enhanced chemical vapor deposition (PECVD) technology.

The laboratory OTR of SiOx film can reach 0.2 cc/m²/day, while maintaining a physical light transmittance of over 89%.

The surface tension of inorganic coatings is extremely high; if it does not reach 45 dynes/cm, microscopic coating detachment can easily occur.

SiOx coatings face physical risks of microscopic network cracks during heat sealing; if the heat sealing mold temperature exceeds 180°C, the local OTR at the sealing edge can increase by over 20%.

During printing and bag making, a 1.5-micrometer thick polyurethane (PU) physical protective liquid must be added to the coating surface.

• RH 0% state: EVOH OTR 0.05 cc/m²/day
• RH 65% state: EVOH OTR 0.15 cc/m²/day
• RH 80% state: EVOH OTR 1.20 cc/m²/day
• RH 90% state: EVOH OTR 4.50 cc/m²/day

In dry lamination processes, the machine application amount of solvent-based adhesives is strictly controlled between 2.5 to 3.5 g/m².

An excessively thin adhesive layer will result in an interlayer peel strength below 1.5 N/15mm, allowing gas molecules to easily permeate laterally through microscopic crystalline voids in the composite layer.

Solvent-free lamination processes reduce the amount of polyurethane adhesive to 1.2 to 1.8 g/m², and the chemical curing time typically needs to reach over 48 hours.

After the two-component polyurethane undergoes complete cross-linking reaction in a 40°C to 50°C curing room, the previously weak lateral gas permeability can be further reduced by 15%.

The pressure difference generated by coffee beans of different roast depths inversely demands the pressure bearing limit of the film.

For dark roasted beans with Agtron values below 50, the outgassing volume can reach 15 L/kg, and the internal pressure of the packaging will peak at 20 mbar within 48 hours after sealing.

The tensile elongation of the material must reach over 100% to prevent microscopic fracture of the barrier layer due to pressure expansion.

The packaging seal width is usually set between 7 to 10 millimeters, and a cross-mesh or straight-line pattern is used on the metal sealing mold.

A pressing temperature of 160°C to 170°C can form a uniform physical melt zone approximately 20 micrometers thick in the PE heat seal layer.

Valve Airtightness

Roasted single-origin Arabica beans release approximately 3 times their own volume of carbon dioxide within 72 hours.

A one-way degassing valve is installed on the surface of the high-barrier film, with its internal physical seal maintained by extremely thin, high-viscosity silicone oil.

Swiss WIPF standard valves require silicone oil to be precisely controlled within a physical range of 1000 to 1500 cSt (kinematic viscosity).

The silicone oil layer adheres to a polyethylene (PE) rubber gasket in a static state, blocking external air.

When the accumulation of carbon dioxide inside the packaging causes the pressure to reach a threshold of 2.0 to 4.0 mbar, the gas physically pushes open the rubber gasket.

The one-way structure instantly opens, and the internal gas is discharged outward at a flow rate of 0.5 to 1.5 liters per minute.

When the internal gas pressure drops to the closing threshold of 0.5 to 1.5 mbar, the gasket resets due to physical rebound force and the surface tension of the silicone oil.

The exhaust closing cycle is usually completed within 0.2 seconds.

Laboratory data shows that structures using high-purity silicone oil experience less than 0.01 cc/day oxygen penetration after 1000 opening and closing cycles.

When exposed to storage environments above 35°C, low-purity silicone oil experiences a mass loss of approximately 2% per month.

The volatilization rate of dimethyl silicone oil at 25°C is below 0.05%, and the physical residual amount is sufficient to support a long-term shelf life of over 12 months.

After coffee beans are ground into powder, extremely fine particles can enter the valve base with the airflow. The Italian Goglio valve system uses a nylon filter screen with a pore size of 10 to 15 micrometers.

The filter screen is fixed to the base bottom with polyurethane hot melt adhesive, achieving over 99% physical interception and maintaining the flatness of the silicone oil layer surface.

• Filter material: Pure nylon monofilament woven
• Pore size specification: 10µm to 15µm
• Thickness control: 0.15mm to 0.20mm
• Air permeability: > 500 cm³/cm²/s (200Pa pressure difference)

A high-frequency oscillator generates mechanical vibrations of 20 kHz to 40 kHz, converting electrical energy into thermal energy.

The polyethylene (PE) or polypropylene (PP) heat seal layer instantly melts within 0.3 seconds, undergoing molecular-level physical cross-linking with the base.

The amplitude of ultrasonic welding is set at 30 to 50 micrometers. The downward pressure applied by the welding cylinder is maintained between 200 to 300 Newtons (N).

After the molten area cools, the tensile failure strength at the joint must exceed the safety standard of 45 N/15mm to resist physical tearing during transportation.

Too low welding temperature leads to physical cold welding. In the ASTM F2096 pressurized bubble test, 10 kPa pressure is charged into the bag, and cold welded locations produce continuous bubble leakage within 5 seconds.

A tiny 0.1-millimeter physical gap causes the internal oxygen concentration to soar from 0.5% to 5.0% within 48 hours.

The pure aluminum foil (AL) layer subjected to continuous high-frequency vibration exceeding 0.5 seconds undergoes brittle fracture of its metallic crystal structure.

Tiny cracks appear at the outer edge, and the overall Oxygen Transmission Rate (OTR) deteriorates to over 2.0 cc/m²/day.

• Vibration frequency deviation > ±0.5 kHz: Leads to uneven melting
• Welding time > 0.6 seconds: Barrier layer thermal perforation occurs
• Downward pressure < 150 N: Insufficient physical cross-linking strength
• Holding time < 0.1 seconds: Melted layer cools and rebounds, causing stringing

The installation speed of the bag making machine introduces additional physical variables to airtightness. High-speed pressing frequency reaches 60 to 80 units per minute.

If the displacement deviation during mechanical arm gripping exceeds 0.5 millimeters, the ultrasonic welding head cannot precisely cover the annular welding rib. Eccentric welding causes the single-side bonding force to be as low as below 10 N/15mm.

The physical shrinkage rate of the polyethylene base during injection molding is controlled between 1.5% to 2.0%.

If the mold cooling water temperature deviation exceeds 5°C, the bottom flange will produce physical warpage greater than 0.05 millimeters.

Drastic changes in ambient atmospheric pressure create inverse physical extrusion on the structure. For every 1000 meters increase in altitude, atmospheric pressure drops by approximately 100 hPa.

The low-pressure environment in aircraft cargo holds causes the gas inside the bag to expand sharply. When the internal pressure exceeds 5.0 mbar, the gasket remains forcibly open for an extended period.

Continuous forced venting consumes the internal silicone oil reserves. After a 12-hour flight, continuous physical airflow reduces the amount of silicone oil coating from an initial 5 milligrams to 2 milligrams.

After landing at sea level standard atmospheric pressure, the thinned coating cannot prevent air from permeating backward.

• Altitude 2000 meters: Internal/external pressure difference increases by 200 hPa
• Cargo hold temperature 5°C: Silicone oil kinematic viscosity increases by 30%
• 12-hour flight: Silicone oil physical loss rate 5%
• Sea level reset: Closing response time delayed by 0.1 seconds

Within 21 days after roasting, carbon dioxide release enters a physical decay period.

The internal packaging no longer generates enough pressure to push open the gasket, and the micro-environment enters a complete static sealing phase. At this point, airtightness relies on the precise physical fit between the polyethylene base and the gasket.

Polyethylene material undergoes physical aging after 6 months of storage.

The Shore A hardness of the gasket increases from an initial 40 degrees to 45 degrees, and its elasticity shows a measurable decline.

The microscopic molecular chains of the outer shell contract, and the closing threshold drifts from 1.5 mbar to 2.0 mbar.

Tiny parameter drift accumulates physical permeation risks during long-term storage. When the closing threshold is higher than the internal pressure, slight physical vibrations break the surface tension of the silicone oil layer.

Gas chromatography analysis of internal gases in retained packaging samples shows that residual oxygen increases linearly at a rate of 0.05% per month.

Biodegradable valves use polylactic acid (PLA) as the injection molding base material. PLA undergoes physical softening when ambient temperature exceeds 45°C.

Under the ASTM D6400 test standard, PLA structures in industrial composting environments at 60°C and 90% humidity undergo physical disintegration into water and gas within 45 days.

The Oxygen Transmission Rate (OTR) of PLA material at room temperature is approximately 30% higher than that of polyethylene.

Engineers increase the thickness of the PLA base from a conventional 0.8 millimeters to 1.2 millimeters.

The increased thickness design extends the physical path of oxygen penetration, controlling the overall gas permeation to within 0.5 cc/day.

Secondary Seal Rate

Laboratory gas analysis shows that within 30 seconds after opening the bag, the oxygen concentration inside the bag rises from 0.5% to near ambient levels of 20.9%.

After air enters, the lipid oxidation rate in coffee increases by approximately 3 times, and volatile aromatic compounds (VOCs) are lost by approximately 15%–25% within 24 hours.

A food packaging storage experiment in California, USA, recorded: VOCs total decreased by 32% in unsealed coffee bags within 48 hours; packaging with a sealing zipper showed a decrease of about 11% under the same conditions.

In packaging engineering, secondary sealing performance is usually measured by the Air Exchange Rate.

A standard 250g coffee bag has an internal volume of approximately 900–1100 ml. If the sealing structure allows 20 ml of air exchange per hour, the oxygen concentration inside the bag will return to over 85% of ambient concentration within 48 hours.

Factors affecting the air exchange rate mainly come from the mechanical precision and material elasticity of the sealing structure.

• Zipper pitch: 0.8–1.2 mm
• Zipper track height: 1.6–2.0 mm
• Biting pressure: 20–35 N
• Seal line length: 80–120 mm
• Allowed gap per closure: < 0.05 mm

Industrial-grade zippers, designed with a double-track structure, extend the air path to approximately 6–8 mm.

The diffusion time of gas in this path can be increased by approximately 70%.

North American Food Packaging Association (FPA) test data shows: The air permeability of a double-track zipper structure is approximately 0.8 ml/hour; a single-track structure is approximately 2.5 ml/hour.

The most common repeated sealing methods for coffee bags include zippers, tin ties, and hook-and-loop structures.

The mechanical sealing degree of the three differs significantly, showing different performances in gas exchange experiments.

Tin tie seals are common in paper coffee bags, and their structure relies on folding metal strips to form a mechanical compression.

Tin ties are typically 0.28–0.35 mm thick, and when folded, they form two or three layers of paper pressed tightly.

Due to microscopic pores between paper fibers, gas can still diffuse into the bag.

UK packaging laboratory tests: The average air leakage rate of a tin tie seal folded three times is approximately 5 ml/min, about 10 times that of a zipper structure.

After bending metal approximately 50–80 times, plastic deformation occurs, and the folding angle cannot restore the original compression force, causing the gap to widen by about 0.1 mm, and air exchange volume to increase by approximately 40%.

Hook-and-loop structures use nylon hook and loop fibers to form a mechanical bite.

Hook fibers are approximately 0.4–0.6 mm long, and loop fibers are approximately 0.15 mm in diameter.

In a fully closed state, the number of hook and loop connection points can reach 300–500 per square centimeter.

• Hook-and-loop bite strength: 6–10 N/cm²
• Repeated opening and closing life: 5000 times
• Retention rate after coffee powder contamination: 80%

Coffee powder particles typically range from 80–300 micrometers in diameter and can easily enter the zipper track.

When fine powder accumulates in the sealing area, a micro-gap of approximately 20–40 micrometers forms between the tracks.

The gas diffusion coefficient in this environment increases by approximately 2 times.

German Packaging Materials Research Institute report: After 0.5 mg of coffee powder accumulates in the zipper track, the air permeability increases from 1 ml/hour to 2.8 ml/hour.

To reduce powder contamination, some packaging designs place the zipper approximately 15–25 mm below the bag opening.

After consumers tear open the bag, less coffee powder enters the zipper area, and the tracks maintain good mechanical biting precision.

Zipper width is usually 8–12 mm, and a wider structure can increase the contact area.

When the width is increased to 12 mm, the track contact area increases by about 30%, and the sealing pressure distribution is more uniform.

Data from the Packaging Testing Center in Illinois, USA, shows: A 12 mm wide zipper reduces air exchange rate by approximately 25%.

Zippers are usually fixed to the PE inner layer by heat pressing.

The sealing temperature is set between 150–170°C, and the seal width is approximately 8–10 mm.

If there are unfused points in the sealing area, air will permeate along the seal edge.

• Heat sealing temperature: 150–170°C
• Pressing time: 0.6–0.9 s
• Sealing pressure: 0.3–0.5 MPa

Heat seal strength is tested according to ASTM F88 standard.

The peel strength of the seal needs to reach 20–30 N/15mm to ensure that the zipper does not delaminate during long-term use.

ASTM test report shows: When peel strength is below 15 N/15mm, zipper seal edges show separation after approximately 200 openings and closings.

Consumer habits also change sealing performance. Households open coffee bags 1–2 times a day on average, and a 250g package is usually consumed within 10–14 days. If each opening lasts 20 seconds, the amount of air entering is approximately 40–60 ml.

Continuous laboratory tests show:

• Day 1: Oxygen concentration 2%
• Day 3: Oxygen concentration 6%
• Day 7: Oxygen concentration 12%

When oxygen concentration exceeds 10%, the oxidation rate of unsaturated fatty acids in coffee significantly increases.

In sensory tests, the aroma intensity score decreased by approximately 18% on average after 7 days.

To extend aroma retention time, some European brands add a secondary folded sealing structure outside the zipper. Consumers close the zipper and then fold the bag opening twice. This double sealing structure can further reduce the air exchange rate by about 35%.

The Italian Packaging Research Center recorded: The zipper + folded structure maintained an oxygen concentration below 5% inside the bag during a 72-hour storage experiment.

The elastic modulus of multi-layer composite films is usually 150–250 MPa.

Softer materials can fit the zipper track when closed, reducing edge gaps.

A composite film approximately 120–140 micrometers thick retains about 90% of its sealing performance after 200 repeated bends; when film thickness is below 80 micrometers, bending fatigue can cause a deformation of about 0.2 mm at the zipper location, increasing air exchange volume by about 30%.

Durability

From Seattle roasteries to London retailers, a single bag of coffee typically undergoes 14 mechanical handling operations and over 480 hours of stacking and compression.

Using an 80-micrometer thick LLDPE (linear low-density polyethylene) inner layer provides over 30 Newtons of puncture resistance, directly resisting the sharp edges of coffee beans.

When the ASTM D882 tensile test data is below 15 MPa, the seam rupture rate of packaging increases to 3.2% when the air pressure in aircraft cargo holds drops to 75 kPa.

Choosing a polymer inner layer is a direct intervention to control physical structural loss to below 0.1%.

Puncture Resistance

Light roasted Ethiopian Yirgacheffe coffee beans have a dehydration rate of approximately 12%, with a single bean density of 0.45 g/cm³, retaining high-hardness sharp edges on the surface.

A single 250-gram bag of coffee, after vacuum sealing, will have the beans pressed tightly against the inner film surface.

The packaging bags, along with pallets, are shipped from the port of Seattle to Hamburg, a 21-day sea voyage accompanied by continuous low-frequency vibrations.

Gravitational force (G-force) can reach 1.5G to 2.0G in waves, and the sharp edges of the beans rub against the same spot dozens of times per minute.

According to the ASTM F1306 slow puncture test standard for films, a puncture probe presses against the film at a speed of 25 mm/min.

Conventional 40-micrometer thick LDPE (low-density polyethylene) can only withstand a peak force of 12-14 Newtons (N).

The deformation of the film before the probe pierces the LDPE layer is 8 millimeters.

Once the film develops micrometer-sized perforations, the oxygen concentration inside the packaging will soar from 0.5% to 21% within 72 hours.

The Flexible Packaging Association (FPA) in North America provides a set of laboratory puncture energy data based on different resin substrates, quantifying the physical response of different materials to the friction of hard coffee beans.

The polymerization method of polyethylene molecules determines the physical toughness of the inner layer.

LLDPE produced with traditional Ziegler-Natta catalysts has uneven molecular chain lengths.

Short molecular chain regions are highly prone to breaking first when encountering concentrated stress generated by bean tips.

Upgrading the comonomer from butene (C4) to hexene (C6) or octene (C8) dramatically increases the number of short branches on the molecular chain.

The puncture energy of C8-LLDPE can reach 0.8 joules (J), an increase of 45% compared to C4-LLDPE.

Metallocene catalysis technology (mPE) changes the distribution of stress on the film.

mPE has a very narrow molecular weight distribution and extremely uniform crystalline structure.

A 50-micrometer thick mPE film can withstand a falling weight of 450 grams without breaking in the ASTM D1709 dart impact test.

When the sharp edge of a bean presses against the mPE inner layer, the film undergoes a high degree of elastic deformation, dispersing physical stress to the surrounding 5 square millimeters area.

Specific resin substrates at 50-micrometer thickness exhibit clear data differences in physical performance:

• C4-LLDPE: Elongation at break 400%, peak puncture force 18 N
• C6-LLDPE: Elongation at break 550%, peak puncture force 26 N
• C8-LLDPE: Elongation at break 650%, peak puncture force 32 N
• Metallocene mPE: Elongation at break 800%, peak puncture force 48 N

Pure mPE has a high coefficient of friction (COF) of 0.5, which causes severe jamming at a film running speed of 120 bags per minute in bag making machines.

Processing plants typically use three-layer co-extrusion technology (A/B/C layers) to formulate the properties of the inner film.

Layer A, close to the aluminum foil, contains 15% LDPE to improve flatness and adhesion with polyurethane adhesive.

The middle B layer, serving as the main stress-bearing skeleton, is injected with 70% mPE to provide extremely high tensile strength.

The C layer, in contact with coffee beans, is mixed with 5% slip agent and antiblocking agent, reducing the static coefficient of friction to 0.2.

The slip agent allows the beans to physically slide when moving inside the packaging bag, significantly reducing the shear force perpendicular to the film surface.

The thickness design of the co-extruded inner layer must strictly match the net weight specifications of the packaging:

• 250g Retail Flat Bottom Bag: Inner layer total thickness 50-60 µm
• 1 kg Cafe Business Pack: Inner layer total thickness 80-100 µm
• 5 kg Bulk Shipping Bag: Inner layer total thickness 120-150 µm
• High-pressure vacuum bag: Requires additional 15 µm nylon layer composite

For completely vacuum-packed brick-shaped coffee bags, atmospheric pressure applies a force of 1 kilogram per square centimeter to the film, pressing it against the bean surface.

Pure polyethylene inner layers undergo cold flow after prolonged pressure, leading to thinning.

By compositing a 15-micrometer BOPA (biaxially oriented nylon) layer above the PE layer, strong intermolecular hydrogen bonds can block physical penetration.

The sharp edges of coffee beans pierce through the 50-micrometer PE surface layer and immediately encounter a nylon isolation layer with a tensile strength of up to 250 MPa.

Puncture test with a probe shows that the puncture force of BOPA/PE composite structure exceeds 60 N.

Several large roasters in Brooklyn, New York, for their long-haul containers to the Middle East, mandate packaging with nylon-containing physical barriers.

The internal structure combination solutions for different processes are as follows:

Quality inspection before shipment uses the ISTA 3A standard test, simulating the transit process within the FedEx system.

The test includes 17 free drops from a height of 46 centimeters onto a steel plate at different angles.

At the moment of impact, the coffee beans inside the packed bag, filled with light roasted beans, will exert instantaneous and severe physical impact on the bottom inner film due to inertia.

Heat Seal and Pressure Resistance

Freshly roasted French roast coffee beans packed in a flat bottom bag with a degassing valve can release carbon dioxide and trace volatile gases equivalent to three times the volume of the beans themselves within 24 hours.

Cargo shipped from sea level Seattle to Denver, Colorado, at an altitude of 1609 meters, experiences an external atmospheric pressure drop from 101.3 kPa to 83.4 kPa.

The gas inside the bag rapidly expands, applying continuous outward peeling force to the heat-sealed seams at the bottom and sides.

Laboratories use ASTM F2054 standard for internal pressure burst testing.

A probe penetrates the center of the packaging bag and injects compressed air at a rate of 10 millibars per second until the seal breaks.

A 340-gram capacity stand-up pouch must withstand a limit pressure exceeding 45 kPa at the bottom cross-fold.

If the heat seal adhesion of the inner LLDPE is improperly set, the seam can develop physical micro-channels prematurely at 30 kPa.

The high-temperature heat sealing knife of the bag making machine presses the film composite layers at a frequency of 120 times per minute. The polymer inner layer must have a very low seal initiation temperature (SIT).

The SIT of metallocene polyethylene (mPE) ranges from 95°C to 105°C, which is 15°C lower than low-density polyethylene (LDPE).

Low SIT shortens the contact dwell time of the heat sealing knife to 0.4 seconds, preventing the outer PET layer from scorching and discoloring under the 200°C high-temperature knife head.

Commercial packaging workshops test 15-millimeter wide seal edge samples using a tensile testing machine:

• Cold Seal Peel Force: After cooling to room temperature, tensile force stabilizes at 20-25 N/15mm
• Hot Tack: Instantaneous tensile force reaches 12 N/15mm within 0.1 seconds after heat sealing
• Seal Window Tolerance: Maintains uniform fusion strength in the 110°C-140°C range
• Resin Melt Index (MI): Set at 2.0 g/10min to optimize flowability
• Heat Seal Layer Thickness Distribution: Accounts for 15% to 20% of the total inner layer thickness

Hot Tack primarily governs the physical tensile state of the packaging bag immediately after sealing, when the resin has not completely cooled.

As the bag drops from the forming tube to the conveyor belt, the gravity of the internal 340 grams of coffee beans instantly pulls at the bottom seal.

Film modified with octene copolymer (Plastomer) has a hot tack strength of up to 15 N at 110°C.

The bottom seam of the packaging bag will not experience 0.5 millimeters of resin slippage under drop impact.

During high-speed screw filling, ground coffee powder can generate fine dust particles smaller than 50 micrometers in the air.

Dust adheres to the electrostatic field at the opening of the film, obstructing smooth heat sealing between resins. When conventional PE film has dust trapped in the seal, the tensile peel strength can plummet from 25 N to 8 N.

Ionomer can completely encapsulate dust particles in its molten state at 120°C.

Physical performance test of polymer heat seal layer under dust particle contamination:

• Conventional LLDPE Resin: Peel strength drops to 8 N/15mm under dust contamination
• Metallocene mPE Resin: Peel strength maintains 14 N/15mm under dust contamination
• Ionomer Resin (Surlyn): Peel strength reaches 22 N/15mm after penetrating dust
• EVA Copolymer Resin: Provides a compromising adhesion of 18 N/15mm

The four corner folds of flat bottom octagonal bags cumulatively have four layers of composite film structure.

Local thickness abruptly increases from 120 micrometers to 480 micrometers, forming an extremely steep stepped physical discontinuity.

The heat sealing knife applies a surface pressure of up to 0.6 MPa during the 0.5-second mechanical compression period.

The molten resin must flow rapidly like a liquid and fill the discontinuity gaps.

Highly fluid polyolefin elastomer (POE) can achieve perfect gap filling, cutting off capillary air leakage paths.

Cargo hold temperatures in transoceanic containers in the equatorial Pacific can remain at 45°C for three consecutive weeks.

Continuous high temperatures soften the amorphous regions of polyethylene, causing the cured heat seal strip to creep under internal carbon dioxide pressure.

According to ASTM F1140 creep test requirements, a constant internal pressure of 20 kPa is applied continuously for 12 hours.

The seal edge slippage of highly crystalline linear polymer inner layers at high temperatures does not exceed 1 millimeter.

Oil Degradation Rate

French Roast treated Arabica coffee beans undergo intense Maillard reactions in a 225°C roaster.

The cell walls inside the beans rupture, and 15% to 20% of the total weight of lipids are forcibly squeezed to the surface.

Within 48 hours after roasting, the thickness of free fatty acids and triglycerides covering the surface of a single bean can reach 0.5 millimeters.

After being packed into bags, over 80% of the inner film will be in 24-hour physical contact with high concentrations of coffee oils for up to 90 days.

The macromolecular chain structure of low-density polyethylene (LDPE) is relatively loose, and intermolecular gaps are sufficient for small molecule free lipids to permeate.

In a 25°C room temperature storage environment, oil permeates into the polymer at a molecular level at a rate of 0.02 millimeters per day.

When the permeation rate reaches 3% of the total polymer volume, the physical extensibility data of the film will plummet from 300% elongation to 150%.

According to ASTM D543 plastic chemical resistance test standard, LDPE immersed in coffee oil for 30 days shows a volume swelling rate of 4.5%.

Structural swelling causes the coefficient of friction (COF) of the film surface to increase from 0.2 to 0.6.

When the bag making machine operates at 100 bags per minute, the film surface becomes sticky, causing the equipment’s film feeding to jam.

The permeation process not only changes the mechanical morphology of polyethylene but also causes physical displacement to deeper layers of the packaging structure.

Composite films typically come from 20 Portland roasteries producing French dark roasted Sumatra Mandheling coffee beans, where the total lipid content after dehydration reaches 18% to 22%.

Within the first 72 hours after bagging, the micropores on the bean surface continuously exude free triglycerides and linoleic acid.

In a single 340-gram retail package, approximately 15 grams of pure oil will broadly adhere to the physical contact surfaces of the inner plastic film.

Conventional low-density polyethylene (LDPE) has a relatively loose molecular chain arrangement, and its amorphous regions are highly susceptible to absorbing free fatty acid molecules.

According to the ASTM D543 standard for evaluating plastic chemical resistance, a 50-micrometer thick LDPE film is fully immersed in coffee extraction oil for 60 days.

The elongation at break of the test sample plummeted from an initial 500% to 220%, indicating a sharp decline in physical tensile data.

“After long-term contact with vegetable oils, the amorphous regions of polyethylene substrates undergo volume expansion, with swelling rates typically fluctuating between 3% and 7%.”

Oil molecules not only remain on the film surface but also penetrate vertically into the material at a rate of 0.02 millimeters per day.

When the penetration depth breaks through the polyethylene layer, triglycerides encounter the two-component polyurethane (PU) adhesive responsible for bonding the aluminum foil (AL) to the inner film.

When packaging bags are displayed on California supermarket shelves on day 45, the previously tightly bonded composite film shows visible bubbling.

Laboratory tensile testing machines track changes in interlayer peel strength; healthy composite layers not affected by oil maintain a tensile strength of over 2.5 N/15mm.

Samples degraded by oil show interlayer adhesive peel strength falling below the industrial passing line of 0.5 N/15mm.

Different forms of fatty acids exhibit quantified differences in their destructive power on polymer films at the molecular level:

• Palmitic acid (C16:0): Saturated fatty acid, penetration rate 0.015 g/m²·day, less destructive
• Linoleic acid (C18:2): Polyunsaturated fatty acid, penetration rate 0.082 g/m²·day, highly susceptible to oxidative degradation
• Oleic acid (C18:1): Monounsaturated fatty acid, primary cause of adhesive swelling, leading to wrinkling
• Chlorogenic acid degradation products: Extremely acidic, accelerating the chemical hydrolysis process of polyurethane hardeners

For Italian blended beans with high oil density, packaging engineers abandon conventional LLDPE and instead use cast polypropylene (CPP) as the first contact layer.

CPP has a molecular structure with much higher crystallinity than PE, and its melting point is above 160°C.

After 14 days in a 60°C high-temperature accelerated aging test oven, the oil penetration rate of a 30-micrometer CPP film was only one-quarter of that of an LDPE sample.

Some packaging with strict requirements for physical softness will use a mixed resin co-extrusion formulation to resist oil degradation.

Incorporating 20% high-density polyethylene (HDPE) into the inner layer material can effectively increase the density of crystal arrangement.

HDPE molecular chains act as a physical barrier, extending the penetration path of free lipids by approximately 3.5 times, significantly delaying the onset of interlayer delamination.

“If metallocene-catalyzed elastomer (POE) is added to the surface layer of co-extruded film, it can not only block triglycerides but also reduce the coefficient of friction by 0.15.”

FDA CFR 177.1520 standard sets extremely high upper limits for hexane extractables in polyolefin resins contacting food.

If free oils extract low-molecular-weight additives from the film, it can produce a faint plastic odor and contaminate the coffee beans themselves.

Using a high-purity ionomer (Ionomer) coating can control the total hexane extractables to below 1.5% while providing heat seal strength.

Laboratory data clearly shows the physical degradation state of different contact layer materials after a 120-day test cycle:

• Conventional LDPE Layer: Thickness swelling 6.2%, interlayer peel strength 0.4 N/15mm
• LLDPE/HDPE Blend Layer: Thickness swelling 2.8%, interlayer peel strength 1.6 N/15mm
• Pure Cast CPP Layer: Thickness swelling 0.9%, interlayer peel strength 2.3 N/15mm
• Surlyn Ionomer: Thickness swelling 0.5%, interlayer peel strength 2.6 N/15mm

Seattle’s specialty coffee brands ship products to Dubai year-round, where container internal temperatures of up to 45°C in summer greatly accelerate the activity of oil molecules.

According to the Arrhenius equation, for every 10°C increase in ambient temperature, the chemical reaction rate and lipid penetration rate double.

European packaging material suppliers have developed a five-layer film structure with co-extruded polyvinyl alcohol (EVOH).

The oxygen transmission rate (OTR) of EVOH is extremely low at 0% relative humidity, and its dense hydroxyl structure has a natural physical repulsion for non-polar triglycerides.

Sandwiching it between two LLDPE layers ensures that even if the surface PE layer is completely permeated by oil, the oil barrier layer can completely block free acids at the physical interface.

“Solventless Lamination technology uses aliphatic polyurethane instead of aromatic adhesives, improving oil resistance by 40%.”

Aliphatic polyurethane molecular chains do not break down when exposed to six months of oil immersion from Italian dark roasted beans.

In peel strength tests, conventional adhesives showed large areas of bubbling on day 90, while samples using solvent-free aliphatic PU maintained a tensile strength of 2.0 N for a 15-millimeter test strip even on day 180.

Bag manufacturers further consolidate the physical stability of the interlayer structure by adjusting the adhesive coating weight from 1.5 g/m² to 2.2 g/m².