Two pouches can look identical on a shelf and behave completely differently in use. One keeps coffee aromatic for eighteen months; the other lets it go flat in six weeks. The difference is rarely the pouch shape or the print — it is the material structure hidden inside the film. Below is a practical breakdown of the six materials that show up most often in flexible packaging, what each one contributes to a laminate, and where each one runs into limits.
How a laminate is actually put together
Before comparing materials, it helps to understand that most flexible packaging is not one material but a stack of them, each doing a specific job. A typical structure has three functional positions:
- Outer layer — carries the print, resists scuffing and gives the pouch its surface feel. PET and kraft paper live here.
- Middle layer — provides the barrier and, where needed, mechanical strength. Aluminium foil, EVOH and nylon sit here.
- Inner layer — the heat-seal layer that closes the pouch and touches the product. PE is the near-universal answer.
Read any structure code — PET/AL/PE, for instance — from outside in. Once you see that pattern, material selection stops being guesswork and becomes a matter of matching each position to what the product needs.
PET (Polyethylene Terephthalate)
Key properties
PET is a polyester film prized for clarity, stiffness and tensile strength. It holds its dimensions under heat, resists oils and most solvents, and takes ink exceptionally well, which is why it dominates the printed outer layer. Typical gauges run from 12µm to 25µm, and it stays serviceable from freezer temperatures up to roughly 150°C.
Where it is used
You will find PET as the outer ply in stand-up pouches, flat-bottom bags and just about any format where shelf presentation matters. It is the standard choice for snack and bakery packaging where the product itself — or a high-quality print finish — is part of the selling proposition.
What to watch for
PET contributes little in the way of barrier, and on its own it does not heat-seal well. It needs to be laminated to a sealant layer, and it offers no meaningful puncture resistance. Treat it as the face of the package, not its armour.
PE (Polyethylene)
Key properties
PE is the workhorse of flexible packaging and the default inner seal layer. Available as LDPE, LLDPE and HDPE, it is soft, tough at low temperatures and seals reliably across a wide heat range. LDPE seals around 105–115°C, HDPE closer to 130°C, and the material stays flexible well below -20°C — the reason frozen-food packaging depends on it.
Where it is used
Almost every laminate ends in PE. Beyond sealing, it appears on its own in heavy-duty bags, mailers and single-layer household formats. It is also the backbone of the mono-material structures now being pushed for recyclability, since an all-PE pouch can in principle enter existing PE recycling streams.
What to watch for
PE has poor oxygen barrier and only moderate grease resistance, so it needs help from other layers in any long-shelf-life application. It also has a lower softening point than PET or nylon, which limits its use in retort structures — those call for CPP instead.
NY / PA (Nylon or Polyamide)
Key properties
Nylon is the material you specify when a package has to survive physical abuse. Its puncture, impact and abrasion resistance are well ahead of PET, and it brings a useful oxygen barrier as well. It handles roughly -60°C to 150°C, which covers everything from deep-freeze to 121°C retort. Common gauges are 15µm and 25µm.
Where it is used
Nylon is standard in vacuum pouches, frozen meat and seafood packaging, and anything with bones, shells or hard edges. It is also the layer that makes boil-in-bag and retort formats viable. We covered the laminate logic behind vacuum formats in Vacuum Pouches: Principles, Materials and Buying Guide.
What to watch for
Nylon is hygroscopic — it absorbs moisture from the air, and as it does, both its barrier performance and its dimensional stability drop. It is also more expensive than PET or PE per kilo. In practice, it is used at the minimum gauge that solves the puncture problem rather than as a bulk layer.
AL Foil (Aluminium Foil)
Key properties
Aluminium foil is the benchmark against which other barriers are measured. At gauges of 7µm, 9µm or 12µm it blocks light, oxygen, water vapour and aroma almost entirely — transmission rates approach zero. It also tolerates retort temperatures without issue, which is why it appears in nearly every sterilizable pouch.
Where it is used
Foil laminates are the default for products where oxidation is the enemy: coffee, tea, milk powder, nuts, pharmaceuticals. If you have read our Complete Guide to Coffee Pouches, the foil layer is what buys that extended aroma window.
What to watch for
Foil has poor flex-crack resistance — repeated bending creates micro-pinholes that quietly destroy the barrier. That is why it is almost always laminated rather than used alone, and why foil pouches need thoughtful handling through distribution. It is also opaque, so you are asking the customer to buy without seeing the product, and it complicates end-of-life recycling.
EVOH (Ethylene Vinyl Alcohol)
Key properties
EVOH is a high-barrier resin used as a thin co-extruded or laminated layer rather than as a standalone film. In dry conditions its oxygen barrier rivals foil, and — critically — it is transparent. That combination makes it the material of choice when you need barrier and product visibility at the same time.
Where it is used
EVOH appears in multi-layer structures for meat, cheese, sauces and prepared foods, typically sandwiched between moisture-resistant layers. It is also central to the shift away from foil: brands that want to cut aluminium while keeping shelf life usually end up specifying EVOH.
What to watch for
EVOH’s barrier is moisture-dependent. Absorb humidity and its oxygen barrier degrades sharply, which is precisely why it is always buried inside the structure behind PE layers. It also adds cost and complexity to recycling, since it is incompatible with both PE and PP streams at any meaningful concentration.
Kraft Paper
Key properties
Kraft paper is made from natural wood pulp and brings strength, a distinctive natural texture and genuine sustainability credentials — it is recyclable in paper streams and can be sourced from certified fibre. In flexible packaging it is used as the outer ply, typically at 40–80 gsm, and laminated to films that supply the seal and barrier functions it cannot provide itself.
Where it is used
Kraft laminates are common for coffee, tea, nuts and dried fruit — categories where a natural, handcrafted look supports the brand story. Our Custom Tea Pouch Packaging Guide goes into how kraft is paired with barrier layers to keep aroma in.
What to watch for
Paper has no heat-seal capability and no meaningful barrier on its own, so a “paper pouch” is always a composite. That affects recyclability in practice, even when the paper itself is recyclable. It also scuffs and absorbs moisture more readily than film, which is worth considering if the product ships through humid conditions.
How to choose the right material for your product
Work through the requirements in this order and the structure usually resolves itself:
- Shelf life and sensitivity — long ambient storage or high fat content pushes you toward foil or EVOH. Short refrigerated cycles can often run on PET/PE alone.
- Physical risk in transit — bone-in, sharp or heavy contents justify a nylon layer. Adding 15µm of PA is far cheaper than paying for returns.
- Processing conditions — retort demands foil or CPP-based structures; boil-in-bag needs nylon; standard dry filling can run on PET/PE.
- Presentation — high-clarity windows point to PET or EVOH. A natural, craft-led look points to kraft.
- Sustainability targets — if recyclability is a stated goal, ask about mono-material PE or PP structures and accept that barrier performance may come down slightly.
The most common mistake is specifying by habit rather than by requirement — defaulting to a heavy foil laminate for a product that would be perfectly stable in PET/PE, or the reverse, under-specifying and discovering the problem after launch.
Where material development is heading
Two trends are reshaping material decisions. Mono-material structures — all-PE or all-PP — have reached the point where their barrier is commercially viable for many products, and they align with regulations such as the EU’s PPWR. At the same time, high-barrier coatings and metallised films are narrowing the gap with foil while keeping packages lighter and easier to process. Neither has made conventional laminates obsolete, but both are worth raising with your supplier before locking in a specification.
Unsure which structure suits your product? Contact Us — we can advise on laminate selection, gauges and cost trade-offs from a production standpoint.