Real Data on Composite Barrier Layers: O2TR Test Comparison of 4 Structures — Paper-Plastic / Aluminum-Plastic / Co-extruded Film
A client selling nuts was originally using paper-plastic composite bags (outer 牛皮纸 + inner PE) and reported that the nuts developed an off-flavor after 3 months, with customer complaints about a "rancid taste." We recommended they switch to aluminum-plastic composite (outer PET + middle AL 铝箔 + inner PE), which is 35% more expensive per unit, but extends the shelf life from 6 months to 12 months. The client ultimately accepted.
The root cause of the "rancid taste" in nuts is the contact between oxygen and oils, triggering an oxidation reaction. To control oxidation, the key is controlling the oxygen transmission rate. The difference in O2TR (oxygen transmission rate) among 4 types of composite material structures is on the order of magnitude—a gap of 100-1000 times. Understanding this data explains why some packaging sells at a higher price while some is cheaper.
Real O2TR Data for 4 Types of Structures
The unit of O2TR is cm³/m²·24h·0.1MPa (how many milliliters of oxygen pass through per square meter per day). The smaller the number, the better the barrier. Below is data from 4 types of structures we tested at third-party labs (data sourced from real reports submitted by inspection clients, accumulated from 2024-2025):
| Structure | Typical Composition | O2TR Value | Corresponding Scenario |
|---|---|---|---|
| Paper-plastic composite | 牛皮纸 + PE | 1500-2500 | Snack outer bags, tea bags |
| Plastic co-extrusion | PE/PA/PE or PE/EVOH/PE | 50-200 | Meat vacuum bags, liquid packaging |
| Aluminum-plastic composite | PET/AL/PE or BOPP/AL/PE | 0.5-5 | Potato chips, nuts, milk powder |
| High-barrier co-extrusion | PE/EVOH/PA/PE multi-layer co-extrusion | 1-10 | Ketchup, juice, liquid soup |
Did you see the comparison between 1500 and 0.5 in the table? That's a 3000-fold difference. These two types of packaging are used for products with "1-month shelf life" and "12-month shelf life" respectively—each fitting its own purpose.
3 Real Cases to Understand Barrier Differences
Case 1: Potato chip bags using paper-plastic, 1-month shelf life
Potato chips are a "high-oil + oxidation-sensitive + crispness-required" product. Paper-plastic composite has an O2TR around 2000, meaning after 1 month, oxygen accumulates inside the bag to a level where the chips oxidize and develop off-flavors. Hence, the shelf life for potato chip bags can only be written as 1 month—after expiry, a rancid taste appears.
But the client has visual requirements—the "牛皮纸 bag" has a better textural appeal than the "aluminum foil bag." In this scenario, a common combination is paper-plastic + inner bag nitrogen-filled + entire bag with an aluminum foil small inner bag (opaque but invisible to consumers). Nitrogen replaces oxygen, essentially combining "outer bag breathable" + "inner bag oxygen-blocking."
Case 2: Milk powder cans using aluminum-plastic, 18-month shelf life
Infant formula milk powder is extremely sensitive to oxygen, because substances produced from whey protein oxidation irritate babies' stomachs. Aluminum-plastic composite has an O2TR between 0.5-1, essentially close to a "complete oxygen barrier" state, with a shelf life of 18-24 months.
There are 3 details in the "aluminum-plastic" structure of milk powder cans that clients often overlook:
- Aluminum foil thickness must be ≥ 7 μm; below this thickness, pinhole rate increases, and O2TR data becomes inaccurate
- Aluminum foil seams must be fully covered with hot-melt adhesive; seam leakage is a real cause of returns
- The sealing ring inside the milk powder can lid (usually EVA or 硅胶) contributes little to the barrier, but has a significant impact on "shelf life after opening"
Case 3: Ketchup using co-extruded high-barrier, barrier does not drop after 121°C retort
Ketchup requires 121°C retort sterilization. Co-extruded film (EVOH barrier layer) loses some barrier performance after retorting, but with EVOH combined with PA, even after 121°C treatment, O2TR can still remain below 10.
EVOH is the core material in "high-barrier co-extruded film," but EVOH is moisture-sensitive—its barrier drops significantly under high humidity. Therefore, co-extruded films are usually made into symmetrical structures PE/EVOH/PE or multi-layer PE/PA/EVOH/PA/PE, allowing PA to protect EVOH from direct contact with water.
2 Scenarios Where It's Easy to Choose Wrong
Scenario 1: Coffee bean packaging with co-extrusion is not enough
Coffee beans continuously release carbon dioxide after roasting (approximately 7-14 days), while oxidation reactions are intense. Co-extruded film O2TR 50-200 cannot block oxidation within 7 days. It is recommended that coffee bean packaging either use aluminum-plastic (like potato chips) or co-extruded bags with a one-way valve (letting CO2 out but keeping O2 out). One-way valve bags have a higher unit price, but solve the special coffee bean requirement of "needing to breathe while fearing oxygen."
Scenario 2: Liquid soup with paper-plastic won't work
A client making ready-to-eat soup packaging chose 牛皮纸/PE composite to pack thick soup. After 3 months, the soup molded. Reason: paper-plastic O2TR is too high, and microorganisms in the liquid multiply when oxygen is present. Liquid soup must use aluminum-plastic or high-barrier co-extrusion for the shelf life to be guaranteed.
The Trade-off Between "Eco-Friendly" and "Barrier"
This is the most frequently asked question by clients—"Aluminum-plastic is not eco-friendly, are there alternatives?"
The real answer has 3 layers:
Layer 1: Alternatives exist, but with boundaries
High-barrier co-extruded film (EVOH or PVDC coating) can replace some aluminum-plastic scenarios. EVOH barrier is close to aluminum-plastic, but costs about 20-40% more, and processing is more difficult.
Layer 2: Biodegradable materials all have relatively weak barriers
PLA, PHA, and other biodegradable materials typically have an O2TR of 500-1000, similar to paper-plastic, suitable for short-shelf-life (1-3 months) products, not suitable for long-shelf-life products.
Layer 3: The cost of recycling
Aluminum-plastic composite bags are a "non-recyclable" structure, because aluminum and plastic cannot be separated. Co-extruded film, if made of a single resin (such as PE/PA/PE), is recyclable. When clients choose "eco-friendly" packaging, they need to be aware that aluminum-plastic has the best barrier but is the hardest to recycle, co-extrusion has sufficient barrier and is recyclable, and biodegradable has weak barrier and only makes sense with industrial composting.
3 Procurement Judgment Criteria
Judgment 1: Look at product shelf life requirements
Within 1 month—paper-plastic/co-extrusion both work; 3-6 months—co-extrusion or aluminum-plastic; over 12 months—aluminum-plastic or high-barrier co-extrusion. Shelf life is the first parameter for barrier selection.
Judgment 2: Look at product form
Powder/granular (milk powder, coffee beans, nuts)—aluminum-plastic; liquid (soup, sauce)—high-barrier co-extrusion; solid snacks (potato chips, biscuits)—aluminum-plastic or co-extrusion + nitrogen flush.
Judgment 3: Look at sterilization method
Pasteurization (80-100°C)—co-extrusion or aluminum-plastic both work; 121°C retort—aluminum-plastic or EVOH high-barrier co-extrusion; room-temperature sterilization (no heat treatment)—aluminum-plastic, co-extrusion carries high risk.
Key Indicators When Submitting for Inspection
When clients submit composite bags for inspection, there are 3 data points to look at on the lab report:
- O2TR (oxygen transmission rate)—as discussed above
- WVTR (water vapor transmission rate)—unit g/m²·24h, key focus for moisture-sensitive products (biscuits, milk powder)
- Heat seal strength—unit N/15mm, ensures the seal is firm
When clients receive the report, send these 3 data points to the product manager or QA, and have them match against their own product's "storage conditions × time × form." If the data aligns, the report is useful; if the data does not match, no matter how expensive the report is, it cannot save the product.
Further reading:
- BOPP / PET / PE / CPP 4 Common Films: How to Choose—Transparency, Stiffness, Heat Seal Temperature 3-Dimensional Comparison + 6 Common Misuses
- How to Calculate Plastic Packaging Migration: 4 Common Migration Tests + Which Category Food/Cosmetics/Toy Companies Should Test
- 甘蔗渣 / PLA / 竹纤维 / 菌丝体: How to Choose Among 4 Bio-Based Packaging Materials?
- Recycled Paper vs. Virgin Paper for Packaging: Real Cost Comparison Across 3 Brand Positioning Categories
FAQ
Can aluminum-plastic composite bags be recycled?
No. Aluminum-plastic composite bags (outer layer PET / middle layer AL / inner layer PE) are a non-recyclable structure because the aluminum foil and plastic cannot be separated. Currently, most recycling systems in China will not accept this type of bag. Some European countries have dedicated "aluminum-plastic separation" recycling pilots, but the recycling cost is high. If a customer's product is being exported to the EU and recyclability is required, consider switching to co-extruded film or a single-resin structure.
Why is EVOH co-extruded film more expensive than aluminum-plastic?
EVOH is an ethylene-vinyl alcohol copolymer. Its synthesis process is complex, and the raw material cost is 3-5 times higher than aluminum foil. At the same time, EVOH co-extrusion requires 5-layer or 7-layer co-extrusion equipment, which means high equipment investment, and the processing fee is also 20-40% higher than aluminum-plastic composite (dry lamination). EVOH's barrier performance is close to aluminum-plastic, but its environmental advantage (recyclability) is the real value.
Why do potato chip bags have to use aluminum-plastic?
Potato chips are a high-oil, oxidation-sensitive product that requires crispness. The O2TR of aluminum-plastic composite is between 0.5-5, which basically completely blocks oxygen, giving a shelf life of 6-12 months. If paper-plastic (O2TR 2000+) is used, the chips will oxidize and go off-flavor within 1 month. The "high" cost of the potato chip bag is exchanged for a sales radius that "can be sold nationwide".
Do I need to look at the "test conditions" on the O2TR report?
Yes, absolutely. Different O2TR test standards give wildly different results. ASTM D3985 (23°C, 50% RH) and ASTM F1927 (23°C, 50% RH, with humidity control) are common methods, and the values are usually close. However, if tested under 90% RH high-humidity conditions, EVOH's barrier performance drops dramatically, with data differing by more than 10 times. When reading a report, look at the "test conditions" first, then compare the "values".
Can biodegradable materials be used for high-barrier packaging?
Currently, no. Biodegradable materials such as PLA and PHA typically have an O2TR of 500-1000, similar to paper-plastic, making them suitable for short shelf-life (1-3 months) products. Biodegradable + high barrier is an industry R&D direction, and some manufacturers are applying coatings or laminations to PLA, but the cost is very high (2-3 times more expensive than aluminum-plastic) and market acceptance is low.
Can nitrogen-flushed packaging replace high-barrier packaging?
It can in some scenarios, but there are limits. Nitrogen flushing reduces the oxygen concentration inside the bag from 21% to 1-2%. Even if the outer bag is permeable, oxidation inside the bag is greatly delayed. Potato chips and nuts commonly use the "nitrogen flush + aluminum-plastic" combination. However, nitrogen flushing cannot completely replace a barrier, because oxygen will slowly permeate in, and long-term storage will still oxidize. Generally, "nitrogen flush + paper-plastic" gives a shelf life of 3-6 months, while "nitrogen flush + aluminum-plastic" can be extended to 12-18 months.
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