Custom Coffee Bags | Light Blocking, Material

Custom coffee bags prioritize Light Blocking​ through specialized materials to protect coffee flavor, as light (especially UV) rapidly degrades volatile aromas. SCA 2022 data shows transparent packaging loses 35% of aromas in 72 hours, with 0.8μg of aromatic compounds escaping per square centimeter per minute.

Pure aluminum foil layers (7-12μm thick) offer a 99.5% light barrier, while nano-coated aluminum films block 98% of UV; German Coffee Lab tests confirm these materials retain 92% of original aroma​ over 30 days, preserving floral, fruity, and chocolate notes. Material choice aligns with roast type and storage goals, ensuring freshness reaches the cup.

Light Blocking

According to a 2022 test by the Coffee Science Foundation (CSF), coffee in transparent packaging loses 35% of its volatile aromas within 72 hours, with 0.8μg of aromatic substances escaping per square centimeter per minute.

A pure aluminum foil layer (7-12μm) has a light barrier rate of 99.5%, and nano-aluminized film has a UV barrier rate of 98%, allowing for 92% aroma retention over 30 days of storage, ensuring the integrity of floral, fruity, and chocolate notes.

Light-Blocking Materials

Pure Aluminum Foil Layer

Pure aluminum foil is the material with the highest light barrier rate among light-blocking materials, with a thickness of 7-12μm (equivalent to 1/10-1/7 of the diameter of a human hair), rolled from high-purity aluminum (above 99.5%).

ASTM D1746 standard tests show a light barrier rate of 99.5% and a UV filtration rate of 99.9%, which can completely block ultraviolet rays (200-400nm) and visible light.

Structurally, aluminum foil is often laminated with plastic layers (such as Al + PE, Al + PET) to solve the issues of pure aluminum being easily folded or susceptible to punctures.

For example, a US packaging company uses a “12μm Al + 25μm PE” composite layer with a tensile strength of 45N/15mm (ASTM D882 standard), suitable for large coffee bean packages over 250g.

Experimental data: In a 2023 test by Coffee Lab in Germany, the same batch of Ethiopian Yirgacheffe (light roast, SCA score 88.5) was packed in pure aluminum foil bags and transparent bags and stored at 25℃ for 60 days.

The volatile aroma retention rate of pure aluminum foil bags was 91%, while transparent bags were only 32%; the acidity retention rate (calculated as citric acid) was 89% for pure aluminum foil bags and 41% for transparent bags.

Applicable scenarios: Specialty single-origin beans (score > 85), award-winning blends, and green/roasted beans requiring storage for more than 6 months. The disadvantage is high cost (30%-50% more expensive than aluminized film), and recycling requires separating aluminum from plastic; some European countries (such as Germany) require the label “Metal Composite Packaging” for classification.

Nano-Aluminized Film

Nano-aluminized film (VM film) is created by vacuum-depositing a nano-scale aluminum layer (approx. 30-50nm thick) onto a plastic substrate (PET, CPP, BOPP), achieving light blocking through metallic reflection.

Common types include VM-PET (Polyethylene Terephthalate substrate) and VM-CPP (Cast Polypropylene substrate).

Parameter comparison (SCA 2023 data):

• VM-PET: Light barrier rate 98%, UV filtration rate 98%, thickness 15-20μm, puncture strength 30N/15mm, cost 40% lower than pure aluminum foil, suitable for drip coffee (10g per bag, requiring lightness and thinness).
• VM-CPP: Light barrier rate 97%, UV filtration rate 97%, thickness 20-25μm, heat seal strength 25N/15mm, softer than VM-PET, suitable for curved packaging (such as round-bottom bags).

Note: The aluminized layer can peel off due to friction (e.g., bags stacking during transport); the surface friction coefficient must be controlled at < 0.3 (ASTM D1894 standard). A US brand used a “VM-PET + Matte Coating” treatment, reducing the friction coefficient to 0.2 and increasing the aluminized layer retention rate by 20%.

Experimental case: Italian illy coffee used VM-PET bags for medium-dark roast blends (Colombia + Brazil); after 30 days of storage, caramel aroma retention was 88% and nutty aroma 85%, with a difference of < 5% compared to pure aluminum foil bags, but with a 35% cost saving.

Dark Ink Composite Paper

Dark ink composite paper consists of Kraft/white cardboard laminated with aluminum foil or aluminized film, with the outer layer printed with carbon black/dark brown ink (hiding power > 90%), reducing light transmission by absorbing light.

Common structure is “Paper + PE + Al + PE,” with a thickness of 80-100g/m² (paper base) + 20μm (aluminum foil layer).

Data: Light barrier rate 85%-90%, UV filtration rate 70% (due to weak absorption of long-wave UV by ink), cost 50% lower than VM film (European Food Packaging Association 2023 quote).

However, the light-blocking effect is limited, making it suitable for low-priced products with short circulation cycles (< 30 days).

Problem: Inks contain VOCs (Volatile Organic Compounds), and EU REACH regulations require limits (< 0.1%); some brands have switched to plant-based inks (such as soybean oil ink), reducing VOC emissions by 60% but increasing costs by 15%.

Case: US brand Folgers instant coffee used “Dark Brown Ink + Aluminum Foil Composite Paper” bags; after 28 days of storage, aroma retention was 75%, which is lower than aluminum foil bags but acceptable for high-volume products due to the $0.1 lower unit price per bag.

UV-Blocking Coated Film

UV-blocking coated film involves coating a resin layer containing benzotriazoles or titanium dioxide onto transparent plastics (such as PET, PP), selectively filtering 200-400nm ultraviolet rays while allowing visible light to pass through (convenient for displaying the product).

Parameters: UV filtration rate 95%, light barrier rate 75% (as visible light can penetrate), thickness 25-30μm, cost 20% higher than VM film.

Coating adhesion must reach grade 4B (ASTM D3359 standard, no peeling in cross-cut test), otherwise, it may peel off and fail.

Applicable scenarios: High-end products needing to display bean color (such as the light brown of light roast beans), combined with nitrogen flushing (oxygen content < 2%), resulting in 80% aroma retention over 30 days.

US brand Stumptown Coffee utilized this solution, setting a 5cm × 5cm transparent window on the packaging, allowing consumers to see the beans while maintaining UV blocking standards.

Impact on Different Coffee Types

Light Roast Single-Origin Beans

Light roast single-origin beans (such as Ethiopian Yirgacheffe, Kenyan AA) rely on citrus, jasmine, and berry aromas, which come from volatile terpenes (linalool, geraniol) and aldehydes (hexanal).

SCA 2022 sensory tests show that when these beans are exposed to natural light (illuminance 500lux), they lose 12%-15% of volatile aromas daily, with only 50% of the initial total remaining after 7 days.

Experimental details: In 2023, the Coffee Science Foundation took Ethiopian Yirgacheffe natural process beans (light roast, SCA score 87) and packed them in transparent bags and pure aluminum foil bags for storage at 25℃. In transparent bags, ethyl acetate (fruit aroma marker) decreased by 62% in 7 days, and linalool (floral aroma marker) decreased by 58%; in aluminum foil bags, both decreased by only 8% and 6%. Regarding acidity, the citric acid retention rate in transparent bags was 41% (89% for Al foil bags), tasting like watered-down juice without any bright acidity.

Applicable light-blocking grade: Must be ultra-strong blocking (> 99%), such as pure aluminum foil or nano-aluminized film (VM-PET), otherwise, regional characteristics will be “erased” by light.

Medium Roast Blend Beans

Medium roast blends (such as Colombia + Brazil, Guatemala + Costa Rica) focus on caramel, nutty, and chocolate aromas, with flavor substances primarily being furans (maltol) and pyrazines (2-ethyl-3,5-dimethylpyrazine), which have more stable molecular structures than those in light roast beans.

A 2023 report from the European Food Packaging Association shows that these beans lose 30% of volatile aromas in 14 days and 55% in 30 days under natural light, twice as slow as light roast beans.

Case: Italian illy medium roast blends (60% Colombia, 40% Brazil) were stored in transparent bags and VM-CPP bags (97% light barrier rate) for 30 days.

In transparent bags, maltol (caramel aroma) decreased by 42%, and nutty pyrazines decreased by 38%; in VM-CPP bags, the decreases were 10% and 12%, respectively. In terms of taste, transparent bags tasted “bland,” like hot chocolate without syrup, while VM-CPP bags could still taste the nutty sweetness of the Brazilian beans.

Applicable light-blocking grade: High blocking (90%-99%), VM film or dark ink composite paper (short-term); aluminum foil is still recommended for long-term storage (> 3 months).

Dark Roast Espresso Beans

Dark roast espresso beans (such as Italian, Indonesian Mandheling) have high roast levels, high oil (triglyceride) content (approx. 16%-18%), and more caramelization products (hydroxymethylfurfural).

A 2023 experiment by Germany’s Coffee Lab found that light activates peroxidase in oils, accelerating oxidative rancidity and decomposing hydroxymethylfurfural (the source of sweetness).

Data: For the same batch of Mandheling dark roast beans (17% oil), transparent bags stored for 21 days saw the peroxide value (rancidity indicator) rise from 0.05meq/kg to 0.32meq/kg (exceeding the 0.25 upper limit of national standards), resulting in a clear rancid smell; VM-PET bags (98% UV barrier) had a peroxide value of only 0.08meq/kg. In terms of sweetness, transparent bags saw a 55% decrease in hydroxymethylfurfural, while VM-PET bags saw a 12% decrease, with the latter still retaining a caramel aftertaste.

Applicable light-blocking grade: High blocking (90%-99%), with aluminum foil or VM film preferred to prevent oils from being “spoiled by sun.”

Drip Coffee

Drip coffee (8-12g per serving) focuses on convenience and has a short circulation period (< 30 days), with flavor dominated by freshly ground aroma. A 2022 test by the All Japan Coffee Association showed that even with basic light blocking (70%-90%, such as black PE bags) combined with nitrogen flushing (oxygen < 2%), the 30-day aroma retention rate can reach 85%.

Comparison experiment: Japanese UCC drip coffee (medium-dark roast blend) was stored in transparent bags, black PE bags (80% light blocking), and VM-PET bags for 30 days.

Transparent bags retained 68% of volatile aromas, with a clear cardboard taste; black PE bags 82%, and VM-PET bags 90%. However, due to fast circulation, the cost advantage of black PE bags (30% lower than VM film) makes them more suitable for mass production.

Applicable light-blocking grade: Basic blocking (70%-90%), dark PE bags or single-layer aluminized film, with the focus on controlling oxygen rather than light.

Coffee Powder

Coffee powder has 5-8 times more surface area than whole beans, leading to a surge in volatile substance exposure to light. A 2023 report from the Flexible Packaging Association noted that for the same beans after grinding, the 24-hour aroma loss rate in transparent bags is 3 times that of whole beans (whole beans lose 10% in 24 hours, powder loses 30%).

Case: Brazilian Santos beans (medium roast) stored in transparent bags as whole beans for 24 hours saw a 12% decrease in linalool; after grinding and being stored in the same bag, it decreased by 38%.

The reason is that the light penetration path for fine particles in powder is shorter, allowing UV to act directly on internal oils.

Applicable light-blocking grade: High blocking (> 90%) is mandatory, and inner aluminum foil bags + outer bags are preferred to minimize powder contact with light.

Basis for Selection

Roast Level and Flavor Compounds

• Light Roast Single-Origin Beans (Ethiopian Yirgacheffe, Kenyan AA): Rely on linalool (floral) and ethyl acetate (fruity); these terpenes and aldehydes lose 12%-15% daily under 500lux natural light (SCA 2022). Materials with a light barrier rate > 99% must be selected, such as pure aluminum foil (99.5%) or VM-PET (98%), otherwise only half the aroma remains after 7 days (Germany Coffee Lab 2023 experiment).
• Medium Roast Blend Beans (Colombia + Brazil): Caramel aroma relies on maltol (furans) and nutty aroma on pyrazines; molecular structures are stable, with 30% loss of aroma in 14 days (European Food Packaging Association 2023). High blocking (90%-99%) is sufficient; VM-CPP (97%) or dark ink paper (85%-90%) are both viable, and cheaper options won’t lose much in the short term (< 30 days).
• Dark Roast Espresso Beans (Mandheling, Italian blends): Oils (triglycerides) account for 16%-18%; light activates peroxidase, causing peroxide values to rise from 0.05 to 0.32meq/kg in 21 days (exceeding the national standard of 0.25), resulting in a clear rancid smell (Germany Coffee Lab 2023). Aluminum foil (99.5%) or VM film (98%) should be used, with a priority on the double protection of oxygen barrier + light blocking.

Data reference: SCA “Roast Level and Flavor Compound Stability Report” 2022

Storage Duration

Case: US brand Counter Culture Coffee used double Al foil bags to store light roast beans for 180 days, with aroma retention still reaching 85% (Brand 2023 storage report)

Material Price and Product Pricing

Light-blocking material costs vary threefold; selection must be reverse-engineered based on the product price.

• Specialty Beans (Price > $15/lb): Use pure aluminum foil bags ($0.3-0.5/bag); although expensive, they have high aroma retention (91%), matching the high price (Blue Bottle Coffee practice).
• Daily Beans ($8-12/lb): Select VM film bags ($0.2-0.3/bag), which save 30%-50% compared to Al foil, with 88% aroma retention over 30 days; consumers cannot distinguish a significant difference (Italian illy medium roast blend case).
• Promotional Packs (Below $5/lb): Use dark ink paper ($0.1-0.2/bag), the lowest cost, accepting 10%-15% aroma loss (US brand Folgers instant coffee uses this solution to dilute costs via high volume).

Material

Aluminum foil composite materials have a light barrier rate of 99.9% (ASTM D1746) and an oxygen barrier < 0.1 cc/m²/day (MOCON test); aluminized film has 95% light blocking (FPA) and 20-30% lower cost;

Dark cardboard composite paper blocks 80% of light when ink coverage > 85% (TAPPI), but oxygen barrier is > 1 cc/m²/day.

Materials must also satisfy puncture resistance > 50N (ISTA transport test) and moisture barrier < 0.1 g/m²/day (ASTM F1249), with solutions selected based on coffee roast level and shelf life.

Material Types

Aluminum Foil Composite Material

The structure usually consists of 3-5 layers: the outer layer uses PET (Polyethylene Terephthalate) or BOPP (Biaxially Oriented Polypropylene) for scratch resistance, the middle layer is a 7-12μm thick aluminum foil (equivalent to 1/10 of a human hair), and the inner layer uses PE (Polyethylene) for heat sealing.

Aluminum foil is key — for every 1μm increase in thickness, the shielding rate against UV (UVB band 280-315nm) increases by approximately 5%.

Dry lamination is used during production, with adhesives bonding the layers firmly. 2023 data from the Flexible Packaging Association (FPA) shows this material has a light barrier rate of 99.9% (ASTM D1746 test), an oxygen barrier < 0.1 cc/m²/day (MOCON coulometric method), and a moisture barrier < 0.05 g/m²/day (ASTM F1249).

For example, Blue Bottle Coffee’s dark roast blend uses aluminum foil composite bags; after 12 months, the peroxide value (POV) was only 2.3 meq/kg (safety threshold < 5), with a flavor loss rate 42% lower than aluminized film (SCAA 2022 comparison experiment).

The disadvantage is high cost, being 20-30% more expensive than aluminized film, and difficult recycling — aluminum foil and plastic layers are hard to separate; the US EPA classifies this as #7 special plastic, requiring transport to specialized recycling plants.

Aluminized Film Composite Material

Aluminized film involves “plating” aluminum onto a plastic film instead of using a whole sheet of aluminum foil. Common substrates are PET (heat resistant) or OPP (cheap), with a vacuum-deposited aluminum layer 30-50nm thick (100 times thinner than aluminum foil). Structurally, it is often two layers: aluminized film + PE inner layer, or a direct three-layer composite (Al-PET/PET/PE).

The light barrier rate depends on the aluminum layer thickness and substrate: PET aluminized film (40nm Al layer) blocks 95% of light (FPA 2023), and OPP aluminized film (35nm Al layer) blocks 92%. The oxygen barrier rate is 0.2-0.5 cc/m²/day (MOCON), slightly weaker than Al foil but sufficient.

US roaster Counter Culture uses PET aluminized film for light roast Yirgacheffe, with an 89% acidity retention rate after 30 days (only 57% for transparent bags).

Costs are 20-30% lower than Al foil, and parts are recyclable (PET aluminized film is #5, OPP is #6), but the Al layer is easily scratched — the light barrier rate may drop to 85% after folding 5 times (ISTA friction test).

Dark Cardboard Composite

Dark cardboard composite relies on “cardboard light blocking + inner film oxygen/moisture barrier.” The cardboard uses SBS (Solid Bleached Sulfate) or unbleached Kraft paper (weight 250-350g/m²), with an inner composite of PE (moisture proof), PET (stiffness), or EVOH (Ethylene Vinyl Alcohol copolymer, oxygen barrier).

Ink is critical — dark colors (black, dark brown) must be used with coverage > 85% (TAPPI T549 test), otherwise the light barrier rate falls below 60%.

For example, US brand Intelligentsia uses unbleached Kraft paper (90% ink coverage) with 80% light blocking and an oxygen barrier of 1.5 cc/m²/day (MOCON). It is suitable for short-term sales (within 6 months), with costs 15-25% lower than aluminized film.

However, it is sensitive to moisture — at 60% ambient humidity, stiffness drops by 30% after moisture absorption (ASTM D3285), leading to easily folded corners during transport.

Nordic brand Kaffa uses FSC-certified cardboard + water-based UV ink, emphasizing “zero carbon,” but the oxygen barrier is 0.5 cc/m²/day lower than PE film composites.

Transparent High-Barrier Material

Transparent high-barrier materials use PVDC (Polyvinylidene Chloride) coating or EVOH co-extruded film, with an oxygen barrier of 0.1-0.3 cc/m²/day (MOCON), but they are completely transparent (light blocking < 10%).

Peet’s Coffee in the US once tried PVDC-coated PET bags for Guatemalan beans; after 72 hours of exposure to sunlight, flavor compounds decreased by 52% (GC-MS detection), forcing a switch back to Al foil composites.

A 5x5cm transparent window on an Al foil bag using EVOH film (oxygen barrier 0.2 cc/m²/day) can balance display and protection.

EU regulation EC 1935/2004 stipulates that the window area must not exceed 15% of the total area, otherwise light blocking fails.

Material Performance

Light Barrier

Light is the slow killer of coffee flavor, especially ultraviolet rays (UVB 280-315nm) and blue light within visible light, which break down flavor molecules like chlorogenic acid and aldehydes. ASTM D1746 (transmission method) is used for testing, where lower values are better.

• Al Foil Composite: 99.9% light barrier (almost total blocking), relying on 7-12μm aluminum foil (1/10 thickness of a hair); for every 1μm of Al foil added, the UVB shielding rate rises by 5%. Blue Bottle dark roast beans in 9μm Al foil bags saw 42% less flavor loss than aluminized film after 30 days of light exposure (SCAA 2022).
• Aluminized Film: 95% light barrier (PET aluminized film, 40nm Al layer), dropping to 85% after 5 folds (ISTA friction test). Counter Culture light roast Yirgacheffe using this material retained 89% acidity after 30 days (only 57% for transparent bags).
• Dark Cardboard: 80% light barrier (ink coverage > 85%, black/dark brown), using SBS cardboard (250g/m²) + PE inner layer. Intelligentsia unbleached cardboard bags saw 28% less flavor compound loss after 60 days in sunlight (GC-MS detection).
• Transparent Material: < 10% light barrier; Peet’s tried PVDC-coated PET bags, which lost 52% of flavor after 72 hours of light, so they now only dare to use 5x5cm windows (accounting for < 15% of bag surface).

Oxygen Barrier

Oxygen causes oil oxidation; a peroxide value (POV) exceeding 5 meq/kg results in a rancid smell. Testing uses MOCON OX-TRAN (coulometric method), unit cc/m²/day (milliliters of oxygen entering per square meter per day).

• Al Foil Composite: < 0.1 cc/m²/day; CRL dark roast Brazilian beans in these bags saw POV rise from 2.1 to 2.5 after 60 days (within safety limits).
• Aluminized Film: 0.2-0.5 cc/m²/day, allowing 2-5 times more oxygen than Al foil, but light roast beans (sensitive to fruit acid) still retained 89% acidity after 30 days.
• Dark Cardboard: 1-2 cc/m²/day; Intelligentsia beans in cardboard bags reached a POV of 3.2 after 60 days, suitable for beans sold within 6 months.
• Transparent High-Barrier: 0.1-0.3 cc/m²/day (EVOH co-extruded film), but useless once light hits, so it is only used for windows.

Moisture Barrier

If ambient humidity exceeds 60%, cardboard absorbs moisture and softens, and beans absorb moisture and mold. Testing uses ASTM F1249 (electrolytic method), unit g/m²/day (grams of water penetrating per square meter per day).

• Al Foil Composite: < 0.05 g/m²/day; Blue Bottle saw a 0.3% moisture absorption rate during transport.
• Aluminized Film: 0.1-0.2 g/m²/day; Counter Culture using this material saw a 0.8% transport damage rate during the rainy season.
• Dark Cardboard: 0.3-0.5 g/m²/day; stiffness drops by 30% after moisture absorption (ASTM D3285), with Kaffa cardboard bags in Danish winter (70% humidity) seeing a 1.5% corner folding rate.
• Transparent Material: 0.1-0.2 g/m²/day, similar to aluminized film, but with high light damage.

Durability

Al Foil Composite: Puncture resistance 55N (using PET outer layer), no damage in 1.2m drop; Blue Bottle annual transport damage rate is 0.3%.

Aluminized Film: Puncture resistance 45N, 0.8m drop easily causes creases, with light barrier dropping 5% after 5 folds.

Dark Cardboard: Puncture resistance 35N, 0.6m drop easily cracks corners; Intelligentsia used thickened SBS board (350g/m²), reducing damage rate from 1.2% to 0.7%.

Transparent Material: Puncture resistance 30N, the least durable, only suitable for short-distance retail.

Environment

Based on EPA classification and compostable certification (ASTM D6400 industrial composting).

• Al Foil Composite: EPA #7 (mixed plastic + Al), requires transport to special recycling plants; US recycling rate < 5%.
• Aluminized Film: PET aluminized film is #5, OPP is #6, recyclable in some cities; recycling rate 15-20%.
• Dark Cardboard: FSC-certified cardboard is #13 (paper), recycling rate 90%+; Kaffa uses this material + water-based ink, with a carbon footprint 30% lower than Al foil.
• Innovative Materials: Germany’s BASF all-PE seven-layer film (oxygen barrier 0.3), recycling rate 50% higher than Al foil; 49th Parallel US uses NatureWorks PLA + EVOH (light blocking 85%), industrially compostable (BPI certification).

Material Selection

Coffee Roast Level

Light roast beans (such as Kenyan AA, Ethiopian Yirgacheffe) have high fruit acid and floral molecules and are sensitive to light — exposure to ultraviolet rays (UVB 280-315nm) for 24 hours causes over 40% loss of chlorogenic acid (SCAA 2022 experiment).

In this case, aluminum foil composite materials (99.9% light barrier, ASTM D1746) are preferred; for example, Blue Bottle light roast beans in 9μm Al foil bags had a 92% acidity retention rate after 30 days (only 58% for transparent bags).

Dark roast beans (such as Italian blends, Brazilian beans) have high oil content (> 16%); oil oxidation producing aldehydes will give beans a “cardboard taste.” Oxygen barrier is more important than light barrier; aluminized film composite materials (oxygen barrier 0.2-0.5 cc/m²/day, MOCON test) are sufficient.

CRL Lab measured: dark roast Brazilian beans in aluminized film bags for 60 days saw POV rise from 2.1 meq/kg to 3.8 meq/kg (safety threshold < 5), with no clear flavor degradation; with Al foil bags, POV only rose to 2.5, making them suitable for dark roast beans with a shelf life over 12 months.

Shelf Life Duration

If coffee is sold within 6 months (such as freshly roasted in a specialty shop), aluminized film composites or dark cardboard composites are more cost-effective.

Aluminized film costs 20-30% less than Al foil (FPA 2023), and its 95% light blocking is enough for daily exposure; dark cardboard (ink coverage > 85%) has 80% light blocking and 15-25% lower costs, like Intelligentsia using unbleached cardboard for beans sold within 6 months, with the damage rate controlled at 0.7% (thickened SBS board 350g/m²).

If you want to store for more than 12 months (such as exports or bulk hoarding), aluminum foil composite materials must be used. SCAA 2022 comparison: the 12-month flavor loss in Al foil bags was 40% lower than aluminized film, with POV always < 3 meq/kg (aluminized film could reach 4.5).

US roaster Counter Culture’s beans exported to Europe all use Al foil composite bags; after 3 months of transport (high sea heat), the flavor score still remained 85/100 (initially 90).

Sales Channels and Environment

Supermarket shelf lighting is strong (usually 500-1000 lux), requiring materials with stable light blocking — aluminized film still blocks 85% after 5 folds (ISTA friction test), more reliable than dark cardboard (which drops to 70% after folding).

Stumptown supermarket versions use PET aluminized film (40nm Al layer); after 30 days of light, the flavor score was 12 points higher than cardboard bags (SCAA blind test).

Specialty shops wanting to display bean color can use Al foil bags with windows — windows use EVOH film (oxygen barrier 0.2 cc/m²/day), with an area not exceeding 15% of the bag surface (EU EC 1935/2004 regulation); like Peet’s limited editions with a 5x5cm window, displaying bean shape while preserving flavor.

Online mailing requires durability; Al foil composite bags have 55N puncture resistance (ISTA 3A test) and no damage in 1.2m drop; Blue Bottle annual transport damage rate is 0.3%; cardboard bags have only 35N puncture resistance, with a 1.5% corner folding rate for long-distance mail (Danish Kaffa data).