How Barrier Films Extend Shelf Life: The Science Behind Food Protection
A deep dive into WVTR, OTR, and multi-layer structures. Learn how to calculate and select the right barrier for 12+ months of freshness.
Written by MyPlast Technical Team
Summary: "Shelf Life" is essentially a battle against time and physics. Barrier films are the shield. This technical guide explains the metrics of WVTR and OTR and helps you choose the right engineered film structure.
The Core Metrics: OTR and WVTR
To spec packaging correctly, you need to speak the language of permeation.
1. WVTR (Water Vapor Transmission Rate)
- Definition: The amount of water vapor that passes through a specific area of film over 24 hours.
- Units: g/m²/24hrs (at tropical conditions usually 38°C, 90% RH).
- Why it matters:
- Too high: Crispy products (chips, crackers) get soggy. Powder products clumps.
- Too high (reverse): Moist products (cakes, wipes) dry out.
2. OTR (Oxygen Transmission Rate)
- Definition: The volume of oxygen that passes through a film.
- Units: cc/m²/24hrs (at 23°C, 0% RH).
- Why it matters: Oxygen fuels bacteria, mold, and oxidizing chemical reactions (rancidity, vitamin loss, color change).
Barrier Material Hierarchy
| Material | Type | Barrier Properties |
|---|---|---|
| Aluminum Foil (7μm+) | Absolute | OTR ≈ 0 | WVTR ≈ 0 (Total Block) |
| EVOH | Transparent Polymer | Excellent O2 barrier, Poor Moisture barrier |
| MetPET (Metallized) | Film | Very High O2 & Moisture (< 1.0) |
| PVDC (Saran) | Coating | High O2 & Moisture (Phasing out due to Chlorine) |
| PE / PP | Base Polymer | Good Moisture barrier, Very Poor O2 barrier |
Designing the Structure (Lamination)
Flexible packaging is a "sandwich" of materials, typically 2 or 3 layers:
Example: Coffee Pouch Structure (Triplex)
PET (12μ) / AL (7μ) / PE (100μ)
- OUTER (PET): Provides heat resistance for sealing jaws and a surface for reverse printing.
- MIDDLE (AL): The functional barrier layer. Blocks everything.
- INNER (PE): The sealant layer. Melts to close the bag and provides mechanical integrity.
Factors Affecting Decision
1. Product Sensitivity
Nuts are high-fat (O2 sensitive). Sugar is hygroscopic (Moisture sensitive). Fresh produce needs to breathe (High OTR needed). Know your product.
2. Storage Conditions
Is the supply chain temperature-controlled? High temperatures accelerate permeation (Arrhenius equation). A film that works in Norway might fail in Dubai.
3. Shelf Life Target
If you only need 3 months shelf life (fast turnover), using Aluminum Foil is over-engineering and wasteful. MetPET might suffice.
Frequently Asked Questions (FAQ)
What happens if OTR is too high for meat?
The meat will turn brown (myoglobin oxidation) and spoil rapidly due to aerobic bacterial growth. Meat requires ultra-high barrier (often with EVOH).
Can I effectively predict shelf life?
Yes, by using permeation calculators and accelerated aging tests in humidity chambers. However, real-time testing is always the gold standard.
Is Metallized film the same as Aluminum foil?
No. Aluminum foil is a solid sheet of metal. Metallized film is plastic with a microscopic vapor-deposited layer of aluminum. Foil blocks light 100%; metallized film blocks ~99%. Foil has zero flex-crack resistance; film is more flexible.
Conclusion
Barrier science is the unsung hero of the food industry. Correctly specifying barrier films prevents food waste and protects brand integrity.
Unsure about OTR/WVTR requirements? Our engineers can analyze your product needs using industry data.
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