Why Barrier Layer Selection Matters
The barrier layer in a thermoforming or lidding film is what determines how long your product stays fresh. The two most commonly specified barrier materials are EVOH (Ethylene Vinyl Alcohol) and PA (Polyamide / Nylon). Choosing between them — or knowing when to combine them — can mean the difference between 7-day and 21-day shelf life.
What is PA (Polyamide)?
Polyamide, also known as Nylon, is the backbone of most thermoforming films. PA provides excellent mechanical properties:
- High puncture resistance
- Outstanding flex crack resistance
- Good oxygen barrier (moderate performance)
- Excellent deep-draw formability
- Thermal resistance for sterilization
PA alone provides an oxygen transmission rate (OTR) of approximately 15–25 cm³/m²/day — suitable for short shelf life products but not adequate for extended fresh food packaging.
What is EVOH?
EVOH (Ethylene Vinyl Alcohol) is a copolymer specifically engineered to provide exceptional oxygen barrier. A thin EVOH layer sandwiched within a multi-layer film structure reduces OTR to 1–3 cm³/m²/day — up to 10× better than PA alone.
- Excellent oxygen barrier (OTR ≤ 3 cm³/m²/day dry)
- Good aroma and flavor barrier
- Transparent and odor-free
- Must be surrounded by moisture-barrier layers (sensitive to humidity)
⚠️ Important: EVOH is hygroscopic — its barrier properties degrade significantly in high-humidity environments if not protected. This is why EVOH is always used as a middle layer, sandwiched between PA and PE/PP layers that protect it from moisture.
Direct Comparison
| Property | PA Only | PA + EVOH |
|---|---|---|
| O₂ Transmission Rate | 15–25 cm³/m²/day | 1–3 cm³/m²/day |
| Puncture Resistance | Excellent | Excellent |
| Deep-Draw Formability | Excellent | Good |
| Shelf Life (Fresh Meat) | 7–10 days | 14–21 days |
| Relative Cost | Lower | Higher (15–30%) |
| Moisture Sensitivity | Low | EVOH layer needs protection |
| Typical Application | Short shelf life, industrial | Premium retail, extended shelf life |
When to Use PA Without EVOH
- Products with shelf life ≤ 10 days
- Products sold and consumed quickly (e.g., same-day deli)
- Cost-sensitive applications where extended shelf life isn't required
- Industrial or non-food applications
When to Add EVOH
- Fresh meat or poultry with 14+ day shelf life target
- MAP (modified atmosphere packaging) applications
- Processed cheese, cured meats, and smoked fish
- Premium retail packaging with strict shelf-life claims
- Products where color retention is critical (e.g., red meat)
Our Film Structures
At ThermoFilmX, we produce both PA-only and PA+EVOH thermoforming films. Our standard structures include:
- PA/PE — standard low-temperature thermoforming film
- PA/EVOH/PE — premium barrier for extended shelf life
- PA/PP — high-temperature retort film
- PA/EVOH/PP — premium retort film with maximum barrier
📋 Our recommendation: If your shelf life target is 14+ days, or if you're packaging fresh red meat, smoked fish, or premium deli products for retail, PA+EVOH is the clear choice. The cost premium (typically 15–30%) is easily justified by reduced spoilage, returns, and extended distribution range.
Need Help Choosing?
Tell us your product, shelf life target, and machine type — we'll recommend the exact film specification.