Barrier Resins and Multilayer Packaging: EVOH, PA and When You Actually Need Them

A barrier resin earns its place only when the product inside is spoiled by gas — oxygen ingress that oxidises fat, carbon dioxide loss that flattens a drink, or aroma escape that dulls a flavour. For oxygen, the strongest transparent barrier resin in commercial use is EVOH (ethylene vinyl alcohol) — the barrier resin EVOH that, in a dry, well-built five-layer structure, cuts oxygen ingress to a tiny fraction of a bare polyolefin film. Polyamide (PA, nylon) sits a step below on oxygen but adds toughness and thermoformability. Neither is a standalone film: both are buried between polyethylene or polypropylene layers and bonded with tie resins. This guide explains what each barrier resin does, the structures they live in, and how to decide when the added layers are worth the cost — and when they are not.

What a “barrier” actually means

“Barrier” is not one property. A package can be a barrier to oxygen, to water vapour, to carbon dioxide, to aroma compounds, to light, or to grease — and a material that is excellent at one can be poor at another. The two numbers that drive most food-packaging decisions are:

• Oxygen Transmission Rate (OTR) — how much oxygen passes through a unit area of film per day, usually reported in cc/m²·day at a stated temperature and relative humidity (commonly 23 °C, and either 0% or 65% RH). Lower is a better barrier.
• Water Vapour Transmission Rate (WVTR) — the equivalent figure for moisture, in g/m²·day.

Because the test conditions change the result, an OTR figure without its temperature and humidity is close to meaningless. The same EVOH grade that reads below 1 cc/m²·day in dry conditions can lose more than 60% of its barrier above 75% RH, as water disrupts the hydrogen bonding that gives EVOH its tightness (TPS — EVOH moisture sensitivity). Always read OTR and WVTR with their stated conditions, and ask the supplier to quote at the humidity your product will actually see.

A useful rule of thumb for ranking transparent oxygen barriers, dry, from weakest to strongest: polyolefins (PE, PP) → PET → PA (nylon) → PVDC → EVOH. EVOH at 32 mol% ethylene offers on the order of 10,000× the oxygen barrier of polyethylene; a 44 mol% grade offers roughly 5,000× (Cloudflex — EVOH barrier guide).

EVOH: the oxygen-barrier workhorse

EVOH is a copolymer of ethylene and vinyl alcohol. The vinyl-alcohol fraction — rich in hydroxyl groups — is what blocks oxygen; the ethylene fraction is what makes the resin meltable and processable. The ratio between them, expressed as ethylene content in mol%, is the single most important number on an EVOH technical data sheet, because it sets the trade-off between barrier and processability.

Ethylene content sets the barrier

Commercial EVOH grades run roughly 27 to 48 mol% ethylene (Gantrade — EVOH overview). The lower the ethylene content, the higher the vinyl-alcohol fraction and the tighter the oxygen barrier — but the harder the resin is to process and the more sensitive it is to moisture. As ethylene content rises, OTR rises (barrier weakens) but processability and moisture resistance improve. Roughly, each 5 mol% increase in ethylene content trades away a meaningful slice of oxygen barrier in exchange for easier extrusion (Cloudflex — EVOH barrier guide).

Barrier rankings are directional and condition-dependent; request grade-specific OTR at your target temperature/RH from the manufacturer’s data sheet.

A 32 mol% film can reach an OTR in the region of 0.3 cc/m²·day at 23 °C and 65% RH (Cloudflex — EVOH barrier guide). For comparison, a bare polyolefin film is hundreds to thousands of times more permeable.

EVOH’s weakness: humidity

EVOH is hygroscopic. Its oxygen barrier is outstanding when dry and degrades as it takes up water, because absorbed water molecules break the inter-chain hydrogen bonding, increase free volume, and open paths for oxygen (TPS — EVOH moisture sensitivity). This has two practical consequences:

1. EVOH must be buried. It is almost never an outer or product-contact layer. It sits in the core, shielded on both sides by moisture-resistant polyolefins (PP or PE) that keep ambient and product humidity away from it (TPS — EVOH moisture sensitivity).
2. Retort is hard on EVOH. During steam retort, water vapour permeates the outer PP and temporarily neutralises the EVOH barrier; oxygen ingress spikes right after retort and the barrier then recovers over roughly 10 to 14 days as the structure re-equilibrates (Packaging Digest — PP/EVOH retort). For retort and microwaveable trays, a symmetric PP/tie/EVOH/tie/PP structure is the standard answer, combining heat resistance with a protected barrier core (TPS — EVOH moisture sensitivity).

This humidity behaviour is why a single OTR number on a spec sheet is not enough: a grade that is superb in a dry snack pack may underperform in a high-moisture, refrigerated, or retorted application.

Polyamide (PA / nylon): toughness plus a useful oxygen barrier

Polyamide — nylon — is the other transparent barrier resin you will meet most often. It does not match EVOH on oxygen: PA’s oxygen barrier is on the order of two magnitudes better than polyolefins, but still 10–100× weaker than high-barrier EVOH (Cloudflex — nylon vs EVOH). What PA brings instead is mechanical performance: very high puncture and abrasion resistance, good aroma barrier, and — critically — excellent thermoformability (Cloudflex — nylon film properties).

PA6 vs PA66 and cast vs oriented

The two common grades are PA6 and PA66. PA66’s denser hydrogen-bond network gives it higher thermal resistance and stiffness; PA6’s looser structure gives more ductility and impact resistance (Zijun — PA6 vs PA66). For packaging, PA6 dominates co-extruded multilayer films because of its forming behaviour (NUREL — PA6 for extrusion).

• Cast PA (CPA) — non-oriented PA6 film with outstanding deep-draw thermoformability, used as the bottom (forming) web in thermoform-fill-seal vacuum packs (NUREL — PA6 for extrusion).
• Oriented PA (OPA/BOPA) — biaxially stretched for higher stiffness and used as a tough lidding or top web.

Like EVOH, PA’s oxygen barrier weakens with humidity, though it is generally less dramatic. Nylon is the right call when you need a combination of toughness, puncture resistance and a medium-to-high oxygen barrier — vacuum, MAP and retort packs in particular (Cloudflex — nylon film properties).

EVOH and PA together

Many high-end structures use both: PA for forming and puncture strength, EVOH for the oxygen barrier. A thermoformed vacuum pack for cheese or processed meat may run, for example, PA/tie/EVOH/tie/PA/sealant — the nylon giving the pack its deep-draw shape and toughness, the EVOH core giving it shelf life.

PVDC, oxide coatings and metallising: the alternatives

EVOH and PA are not the only barriers, and the right answer is sometimes a coating rather than a co-extruded layer.

• PVDC (polyvinylidene chloride) — a high-barrier coating whose stand-out property is that its oxygen and moisture barrier is far less affected by humidity than EVOH, so it holds up in refrigerated and frozen chains (Cloudflex — PVDC film). It is applied as a thin coat on PET, OPP or PA. The trade-off is chlorine content, which complicates recycling and end-of-life — a growing reason converters look for alternatives (Packaging Strategies — PVDC alternatives).
• AlOx / SiOx (transparent oxide coatings) — vacuum-deposited aluminium-oxide or silicon-oxide layers that give high barrier while staying transparent, microwaveable, retortable and metal-detector-safe. They are not heat-sealable and the brittle oxide must be sandwiched between plastic layers to survive handling (e-space / MMU — AlOx barrier coatings).
• Metallised film — aluminium vapour-deposited on a substrate; high barrier and durable but opaque and not thermoformable (e-space / MMU — AlOx barrier coatings).
• Aluminium foil — the absolute barrier (near-zero OTR and WVTR), used where shelf life must be measured in years; opaque, prone to pinholes/flex-cracking, and the hardest to recycle in a flexible laminate.

Why barrier resins live in multilayer structures

EVOH and PA are rarely used alone. A finished pack must also be heat-sealable, moisture-resistant, mechanically tough and printable — jobs no single barrier resin does well. So converters co-extrude several polymers into one film, each layer doing one job.

A typical fresh-produce or food film runs four to seven layers — for example LLDPE / tie / EVOH / tie / LLDPE or LLDPE / HDPE / tie / EVOH / tie / HDPE / LLDPE (Polymerdatabase — multilayer films). The most common arrangement is a symmetric “ABCBA” five-layer structure, with PA or EVOH as the barrier core and polyethylene as the heat-seal skin (Desu Plastic — multilayer coextruded films).

The job of each layer

• Sealant (inner) layer — usually LLDPE or a PP/PE blend; melts to form the seal that closes the pack.
• Structural / outer layer — PE, PP or PET; gives stiffness, print surface and moisture protection.
• Barrier core — EVOH and/or PA; the layer this whole structure exists to protect.
• Tie (adhesive) layers — the unsung resin. Polyolefins do not bond to EVOH or PA, so a tie layer — typically a maleic-anhydride-grafted PE or PP — is needed between each dissimilar pair to stop the layers delaminating (Polymerdatabase — multilayer films). Every barrier core therefore costs you two tie layers as well.

Symmetry matters: a balanced structure such as PP/tie/EVOH/tie/PP distributes stress evenly during forming and stays stable in use, which is why it is the default for retort and microwave trays (TPS — EVOH moisture sensitivity).

These structures are built by LDPE and LLDPE films for food processors, and the barrier core thickness is usually a small fraction of total film — EVOH is the most expensive resin in the stack, so converters use the minimum that delivers the required OTR.

When you actually need a barrier — and when you do not

The honest answer for many products is: you do not. Barrier layers add resin cost, tie-layer cost, processing complexity and recycling difficulty. They pay off only when the product is genuinely oxygen-, aroma- or moisture-sensitive and the required shelf life cannot be met without them.

You probably need an oxygen barrier (EVOH/PA/PVDC) for:
– Fresh and processed meat, poultry and fish (vacuum and MAP).
– Cheese and many dairy items.
– Oxygen-sensitive products: nuts, oily snacks, coffee, products with fats prone to rancidity.
– Long-shelf-life ambient ready meals and retort pouches/trays.

For meat, MAP often runs high-oxygen mixes (e.g. 70–80% O₂ with 20–30% CO₂) to hold colour while inhibiting bacteria, extending shelf life from a few days to up to ~12 days (Agriculture.Institute — MAP for meat). Holding that atmosphere demands a genuine barrier; a “barrier container” is often defined as one with an OTR below ~70 cc/m²·day·atm (FreshProduce — MAP white paper). For longer shelf life, PVDC- or EVOH-based composites are preferred (FreshProduce — MAP white paper).

You probably do not need a high oxygen barrier for:
– Dry, oxygen-stable goods (pasta, rice, sugar) where moisture barrier matters more than oxygen.
– Short-shelf-life, fast-turnover items.
– Fresh produce that must breathe — here you want controlled, even microperforated permeability, not a barrier.

Specify the barrier to the shelf life and the spoilage mechanism, not to a generic “high barrier” request. Over-specifying wastes money on every pack you ship.

The cost lever: how much barrier resin you actually use

The reason barrier specification is worth getting right is that the barrier core is the most expensive resin in the structure, and you pay for it on every single pack. EVOH typically costs several times more per kilogram than the polyolefins around it, so converters keep the core thin — often only a few microns out of a total film tens of microns thick — and use the lowest-cost grade (highest ethylene content) that still hits the OTR target. The economics push in three directions at once:

• Thinner core, higher ethylene content lowers resin cost but raises OTR. The skill is finding the grade and thickness that just meets your shelf life with no margin you are paying for unnecessarily.
• Symmetry adds tie layers. Every buried barrier core needs a tie layer on each side, so the structure carries two adhesive layers per barrier — real cost in both resin and line complexity.
• Recyclability is now a cost too. Mixed-polymer barrier laminates (PE + EVOH + PA + tie) are harder to recycle than mono-material structures, and producer-responsibility schemes increasingly price that in. Where shelf life allows, a high-barrier mono-PE or mono-PP structure with a thin compatible barrier can be the better total-cost answer.

This is why “tell us the shelf life” beats “tell us the barrier”: the same product can be packed in a cheap two-layer film or an over-engineered seven-layer laminate, and the gap between them is pure avoidable cost.

How Innovote sources this

Barrier and multilayer packaging is a structure-engineering problem before it is a procurement one, so we start with the product, not the resin.

1. We define the failure mode. Is the product spoiled by oxygen, moisture, aroma loss, or light — and over what shelf life, at what storage temperature and humidity? That decides whether you need EVOH, PA, a coating, or no barrier at all.
2. We translate shelf life into an OTR/WVTR target at your storage humidity — not a dry-lab number — and let that drive grade selection (for EVOH, the ethylene mol% that hits the target with the least resin).
3. We match the structure to the process. Retort, thermoform-fill-seal, flow-wrap and lidding each favour different layouts (symmetric PP/EVOH/PP for retort; cast PA forming webs for deep-draw vacuum packs).
4. We confirm food-contact compliance on the contact layer. Note the distinction in our food-grade vs food-safe resins guide: a resin being food-grade is not the same as the finished structure being food-safe for your product. Migration behaviour depends on the food, time and temperature — see migration testing and food-contact compliance for the EU 10/2011 and US FDA 21 CFR framework.
5. We document, not assert. Suppliers provide grade technical data sheets and compliance declarations; finished structures are described as compliant with / meeting the requirements of the relevant regulation, with certificates and specs available on request — never as “approved” or “certified” without a basis.

We can quote barrier resins (EVOH, PA6/PA66, tie resins, masterbatch) and finished multilayer film or sheet, with grade, MOQ, lead time and a landed-cost path into Egypt.

Frequently asked questions

Is EVOH or nylon (PA) the better oxygen barrier?

EVOH is significantly better on oxygen — by roughly 10–100× over PA, and thousands of times over plain polyethylene (Cloudflex — nylon vs EVOH). PA wins on toughness, puncture resistance and thermoformability. Many premium packs use both: PA for forming and strength, EVOH as the buried barrier core.

Why can’t EVOH be the outside layer of a pack?

EVOH is hygroscopic — it absorbs water, which disrupts its molecular structure and lets oxygen through, cutting its barrier by more than 60% at high humidity (TPS — EVOH moisture sensitivity). It must be buried in the core and shielded on both sides by moisture-resistant PP or PE.

What is a tie layer and why does every barrier structure need one?

Polyolefins (PE, PP) do not bond chemically to EVOH or PA, so without an adhesive the layers would delaminate. A tie layer — usually a maleic-anhydride-grafted PE or PP — sits between each dissimilar pair to hold the structure together (Polymerdatabase — multilayer films). A single EVOH core therefore adds two tie layers to the structure.

Does retort processing damage the EVOH barrier permanently?

No — it is temporary. Steam during retort permeates the outer layer and neutralises EVOH’s barrier, so oxygen ingress spikes immediately after retort, then the barrier recovers over about 10–14 days as the structure re-equilibrates (Packaging Digest — PP/EVOH retort). Symmetric PP/tie/EVOH/tie/PP structures are standard for retort because of this.

How do I know what OTR my product needs?

Work back from spoilage: define the shelf life you need, the storage temperature and humidity, and how oxygen-sensitive the product is. A common benchmark for a “barrier” pack is an OTR below ~70 cc/m²·day·atm (FreshProduce — MAP white paper); oxygen-sensitive products needing months of shelf life require far lower, which is where EVOH or PVDC come in. Tell us the product and target shelf life and we’ll back-calculate the OTR and the structure.

Is PVDC better than EVOH?

Neither is universally better. PVDC’s advantage is that humidity barely affects its barrier, so it performs in refrigerated and frozen chains where EVOH struggles (Cloudflex — PVDC film). EVOH gives a higher dry oxygen barrier and avoids PVDC’s chlorine content, which is an end-of-life/recycling drawback (Packaging Strategies — PVDC alternatives). The choice depends on your storage conditions and sustainability targets.

Tell us the spec; we’ll come back with the structure

Barrier packaging is easy to over-buy and easy to under-spec. Tell us the product, the shelf life you need, and the storage conditions — and we’ll come back with the barrier resin grade, the multilayer structure, MOQ, lead time and a landed-cost path. Start with our food-grade packaging resins hub for the full resin picture, or compare film constructions in LDPE and LLDPE films for food.

Byline: Innovote Trade Desk. Capability statements describe materials as compliant with / meeting the requirements of the cited standards; certificates and specs available on request. This article is technical guidance, not a certification or a health claim.