High-Barrier Packaging Films: EVOH and Aluminum Foil Barrier Technology Explained
Most flexible packaging films sold today are made from polyethylene or polypropylene. These materials are cheap, easy to extrude, and work fine for dry goods with a short shelf life. But they share a serious weakness: oxygen passes through them freely. A plain PE film has an oxygen transmission rate (OTR) of around 7,000 to 10,000 cc/m² per day. Oxygen penetrates the package within days, causing fats to go rancid, vitamins to degrade, and food to spoil long before the printed expiry date. For any product that needs to survive more than a few weeks on a store shelf, standard PE and PP films simply do not work.
What EVOH Does in a Barrier Film
EVOH stands for ethylene-vinyl alcohol copolymer. It is a transparent thermoplastic that blocks oxygen far better than any standard polyolefin. A thin layer of EVOH — often just 3 to 5 microns thick — can reduce the OTR of a film structure by 100 to 1,000 times compared with plain PE. A PE film that lets 8,000 cc/m² of oxygen through every day can drop to under 10 cc/m² when a proper EVOH layer is added. That is the difference between coffee going stale in a week and coffee staying fresh for six months.
But EVOH has a catch. It is hydrophilic, meaning it absorbs moisture from the air or from the product itself. When EVOH gets wet, its oxygen barrier drops sharply — sometimes by more than 80 percent. A film manufacturer cannot just put EVOH on the outside and expect it to perform. The EVOH layer must be sandwiched between two moisture-blocking layers, typically polyethylene or polyamide (PA), which shield it from humidity on both sides. This is why almost every EVOH-based film from a flexible packaging factory follows a structure like PA/Tie/EVOH/Tie/PE or PE/Tie/EVOH/Tie/PE.
Aluminum Foil as the Premium Barrier
When a product demands maximum protection, aluminum foil is the barrier layer of choice. A foil layer in a flexible film structure has an OTR of effectively zero — provided the foil is intact and free of holes. In a typical PET/AL/PE laminate, the aluminum foil sits between an outer PET layer for printability and an inner PE layer for heat sealing. That 6 to 9 micron foil blocks all oxygen, all moisture vapor, and all UV light in one layer. No plastic barrier film can match that combination.
Foil laminates are the backbone of long-shelf-life packaging. Retort pouches for ready-to-eat meals, coffee bean bags for 12-month freshness, and pharmaceutical blister packs all rely on aluminum foil because no transparent polymer comes close to its barrier performance. A packaging supplier building foil-based laminates can guarantee shelf life measured in years, not weeks.
Pinholes: The Critical Failure Mode in Foil Laminates
Aluminum foil is not invincible. During manufacturing, the foil is rolled to 6 to 9 microns — thin enough that mechanical stress creates pinholes. Foil gets folded during lamination, compressed during slitting, and handled during conversion. Every fold and compression point is a potential pinhole, and every pinhole is a leak path that lets oxygen and moisture straight through.
This is why foil laminate quality depends heavily on the laminating process. A factory using dry-bond lamination with precise tension control and uniform adhesive coating will produce far fewer pinholes than one that rushes the process. Foil suppliers test pinhole counts using backlight inspection, and converters verify barrier performance by testing finished laminates for OTR and WVTR after lamination — not just before.
Clear Alternatives to Aluminum Foil
Some products need barrier protection but also need to be visible to the consumer. For these cases, manufacturers use transparent high-barrier alternatives. Silicon oxide (SiOx) coated PET applies a thin glass-like coating onto a PET substrate, giving an OTR of around 0.5 to 2 cc/m² per day. Metallized PET (VM-PET) deposits a thin aluminum layer under vacuum, bringing the OTR to roughly 0.5 to 5 cc/m² per day. Both let some light through and provide partial barrier performance.
These clear and metallized alternatives work well for products with moderate shelf life requirements. But for anything that needs to sit on a warehouse shelf for a year or survive retort sterilization at 121°C, they still fall short of aluminum foil.
When to Use Each Barrier Option
The choice of barrier layer comes down to the product, the required shelf life, and the packaging process. Roasted coffee beans need aluminum foil — typically in a PET/AL/PE or PET/AL/NY/PE structure — to hold carbon dioxide inside and keep oxygen out for 12 months. Snack products packed with nitrogen flush can use a PA/EVOH/PE coextruded film because the nitrogen flush handles the initial oxygen and the EVOH keeps new oxygen from entering. Retort pouches for sterilized food always need aluminum foil because the high-temperature retort process would degrade EVOH and because the product must remain sterile for the entire shelf life, which only a foil barrier can guarantee.
A packaging manufacturer that understands these trade-offs can guide customers toward the right structure instead of overselling foil where EVOH would do the job, or under-specifying EVOH where only foil will hold up. The barrier film is not just a material choice — it is a shelf-life decision.
References
ASTM D3985-21. Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Detector. ASTM International, 2021.
ISO 15106-1:2003. Plastics — Film and sheeting — Determination of water vapour transmission rate — Part 1: Gravimetric detection sensor method. International Organization for Standardization, 2003.
FPA Flexible Packaging Association. State of the North American Flexible Packaging Industry Report. FPA, 2022.
