Barrier performance is the single most important technical decision in food packaging development, yet it remains one of the least well-documented. Get it wrong and your product loses shelf life, flavour, or texture weeks before it should. Over-specify and you pay for barrier materials you do not need, while also making recyclability harder. This guide gives you a practical framework for matching your product type to the right barrier specification, covering OTR, WVTR, material options, and how to communicate your requirements clearly to a packaging supplier.
What Do We Mean by Barrier Performance?
Barrier performance describes how effectively a packaging film prevents gases, moisture, and light from passing through the material wall. Two metrics define it:
Oxygen Transmission Rate (OTR) measures how much oxygen passes through a film over 24 hours, expressed as cc/m²/day at standard conditions (23°C, 0% RH). Oxygen drives oxidation, which causes rancidity in fats, staling in baked goods, and colour loss in meats and spices.
Water Vapour Transmission Rate (WVTR) measures moisture movement through the film, expressed as g/m²/day at standard conditions (38°C, 90% RH). Moisture ingress causes caking in powders, sogginess in cereals, and mould growth in high-moisture products. Moisture loss causes drying, weight reduction, and texture change in wet products like pet food or confectionery.
The testing standards most widely accepted in the UK and EU are ASTM D3985 for OTR and ASTM F1249 for WVTR. When comparing supplier data sheets, always check that results are quoted at the same temperature, humidity, and film thickness, as these variables dramatically affect the numbers.
Barrier Materials: What Each Layer Does
Flexible packaging films are typically built from multiple layers, each contributing a specific function. Understanding what each material brings to the structure helps you specify intelligently rather than simply asking for “high barrier.”
| Material | Primary Barrier Function | Typical OTR (cc/m²/day, 25µm) | Typical WVTR (g/m²/day, 25µm) | Notes |
|---|---|---|---|---|
| EVOH | Oxygen | 0.01 – 0.5 | 8 – 15 | Best oxygen barrier available. Sensitive to humidity: performance degrades 10-50x at high RH. |
| Nylon (PA) | Oxygen, puncture | 2 – 5 | 15 – 25 | Good oxygen barrier with excellent puncture resistance. |
| PET | Oxygen, clarity | 2 – 8 | 4 – 17 | Moderate oxygen barrier with high clarity and stiffness. Often used as a print web in laminate structures. |
| Metallised PET | Oxygen, moisture, light | 0.5 – 1.5 | 0.3 – 1.0 | Thin aluminium deposition provides excellent all-round barrier at low cost and weight. |
| Metallised OPP | Moisture, light | 50 – 100 | 0.3 – 0.8 | Strong moisture barrier and light block, but limited oxygen barrier. |
| Aluminium foil (6-12µm) | Complete barrier | < 0.01 | < 0.01 | Total barrier to oxygen, moisture, light, and aroma. |
| PE (LDPE/LLDPE) | Moisture, seal layer | 2,000 – 4,000 | 6 – 15 | Poor oxygen barrier but good moisture resistance. |
| HDPE | Moisture | 500 – 1,000 | 3 – 6 | Better moisture and oxygen barrier than LDPE. |
| PP (OPP/CPP) | Moisture | 1,000 – 2,000 | 2 – 6 | Good moisture barrier with low cost. OPP offers clarity and printability. |
These values are indicative and vary by grade, thickness, and manufacturer.
Matching Barrier Requirements to Product Type
Different food products have fundamentally different enemies. A dry snack needs to keep moisture out, while a wet pet food needs to keep moisture in and oxygen out. The table below maps common product categories to their primary barrier needs and typical shelf life targets.
| Product Type | Primary Threat | OTR Target | WVTR Target | Typical Shelf Life | Recommended Structure |
|---|---|---|---|---|---|
| Ground coffee | Oxygen, aroma loss | < 1 cc/m²/day | < 2 g/m²/day | 12 – 18 months | PET / Al foil / PE or PET / MetPET / PE with degassing valve |
| Dry snacks (crisps, nuts) | Moisture, oxygen (fat oxidation) | < 2 cc/m²/day | < 1 g/m²/day | 6 – 12 months | OPP / MetOPP / PE or PET / MetPET / PE |
| Wet pet food | Oxygen, moisture loss | < 1 cc/m²/day | < 2 g/m²/day | 18 – 36 months | PET / Nylon / Al foil / CPP (retort grade) |
| Dry pet food (kibble) | Moisture, fat oxidation | < 5 cc/m²/day | < 2 g/m²/day | 12 – 18 months | PET / PE or PET / MetPET / PE |
| Ready meals (retort) | Oxygen, moisture loss | < 0.5 cc/m²/day | < 1 g/m²/day | 18 – 24 months | PET / Nylon / Al foil / CPP (retort 121-131°C) |
| Protein powder / supplements | Moisture, oxygen | < 2 cc/m²/day | < 1 g/m²/day | 12 – 24 months | PET / MetPET / PE or PET / EVOH / PE |
| Confectionery / chocolate | Moisture, aroma, light | < 5 cc/m²/day | < 1 g/m²/day | 6 – 12 months | OPP / MetOPP / PE |
| Spices and seasonings | Oxygen, aroma, light | < 1 cc/m²/day | < 1 g/m²/day | 12 – 24 months | PET / Al foil / PE |
| Frozen meals | Cold crack resistance, moisture | < 10 cc/m²/day | < 5 g/m²/day | 12 – 18 months | Nylon / PE (cold-resistant grade) |
The EVOH Question: When to Use It and When to Avoid It
EVOH (ethylene vinyl alcohol) is the go-to oxygen barrier layer for applications where aluminium foil is not suitable, for example when you need microwave transparency, retort capability without foil, or a path towards recyclability. A thin EVOH layer (3-5µm) in a coextruded or laminated structure can achieve OTR values below 0.5 cc/m²/day.
However, EVOH has a well-documented weakness: it absorbs moisture, and its oxygen barrier degrades dramatically as relative humidity rises. At 80% RH, EVOH’s OTR can increase by 10 to 50 times compared to its dry-state performance. This means EVOH must always be sandwiched between moisture-resistant layers (PE or PP) that protect it from ambient humidity.
Use EVOH when:
- You need a high oxygen barrier without aluminium
- The product will be microwaved in-pack
- You are targeting a recyclable mono-PE or mono-PP structure (EVOH at less than 5% by weight is accepted in most recycling streams)
- The storage environment is controlled (ambient, not tropical)
Think twice about EVOH when:
- The product will be stored in high-humidity conditions (above 75% RH) for extended periods
- You need a complete light barrier (EVOH is transparent)
- Cost is the primary driver (metallised films are cheaper for equivalent barrier in many applications)
Five Steps to Specify Barrier Performance Correctly
- Identify your product’s primary degradation pathway. Is it oxidation (fats, oils, colour), moisture gain (powders, cereals, snacks), moisture loss (wet products, soft textures), or aroma loss (coffee, spices)? This determines which metric matters most: OTR or WVTR.
- Set your target shelf life. Work backwards from the retail requirement. UK multiples typically expect 12 months minimum for ambient products.
- Quantify the barrier targets. Use the product-type table above as a starting point, then refine with your food technologist based on accelerated shelf life testing.
- Consider the full storage environment. Temperature, humidity, light exposure, and physical handling all affect barrier requirements. A product stored in a chilled supply chain needs different specifications from one sitting in a warm warehouse.
Common Specification Mistakes to Avoid
Over-specifying barrier is just as costly as under-specifying. Requesting aluminium foil lamination for a product that only needs metallised PET adds unnecessary material cost, increases your environmental levy under pEPR, and makes the pack harder to recycle. Equally, specifying EVOH for a product stored in tropical humidity without understanding its moisture sensitivity will leave you with a pack that underperforms its data sheet values.
Another frequent mistake is ignoring the seal layer’s contribution. The inner PE or CPP layer is often treated as “just the seal,” but its thickness and grade directly affect both WVTR performance and seal integrity under filling conditions. A thinner seal layer reduces moisture barrier, while a grade not matched to your filling temperature can cause weak seals and leakers, both of which destroy shelf life far faster than a marginal OTR difference.
Recyclability and Barrier
Multi-material laminates containing aluminium foil will attract higher Extended Producer Responsibility fees under the red/amber grading, while mono-material structures that achieve recyclability will qualify for lower green-rated fees.
The good news is that barrier technology for mono-materials is advancing rapidly. Mono-PE structures with EVOH interlayers (below the 5% weight threshold) can achieve OTR values under 1 cc/m²/day while remaining compatible with PE recycling streams. Barrier coatings such as SiOx and AlOx applied to mono-PE or mono-PP films offer another route, providing oxygen barrier approaching metallised film performance without disrupting recyclability.
How Aropack Can Help
At Aropack, we work with technical and quality managers every day to translate product requirements into packaging specifications that deliver the right barrier performance, at the right cost, with a clear path to recyclability.
Whether you are developing a new product and need help specifying barrier requirements, or you are reviewing an existing structure to improve shelf life or reduce material cost, our technical team can guide you through the options. We supply stand-up pouches, retort pouches rated to 131°C, flat bottom pouches, and recyclable mono-material structures across the full range of barrier specifications.
Get in touch with your product details and shelf life targets, and we will recommend a structure that works.
