Almost every specification argument about film ends up being an argument about three polymers. Polyethylene, polypropylene and polyamide cover the overwhelming majority of primary packaging for frozen and dried food, and they are not interchangeable. A bag that performs for eighteen months at minus eighteen degrees and a bag that performs on a hot fill line are made of different things, and a buyer who specifies by thickness alone will get whichever the converter finds cheapest that week.
This guide compares the three by the properties that actually decide performance, then explains why the answer in practice is usually a laminate, and what the recyclability rules in the packaging and packaging waste regulation do to that answer.
The short version
| Property | PE (LDPE, LLDPE) | PP (CPP, BOPP) | PA (nylon) |
|---|---|---|---|
| Flexibility at minus 18 C | Stays flexible | Stiffens, can embrittle | Stays flexible |
| Oxygen barrier | Poor | Poor to moderate | Good |
| Water vapour barrier | Good | Good | Poor, hygroscopic |
| Puncture and abrasion resistance | Moderate | Moderate | High |
| Sealing | Seals to itself readily, wide window | Narrower window, higher temperature | Does not seal well, needs a seal layer |
| Clarity | Hazy to clear | High clarity, high gloss | Clear |
| Typical role | Seal layer, liner, single-web freezer bag | Outer web, clear pack, higher temperature use | Middle barrier and toughness layer |
Read the table as a description of roles rather than a ranking. PE is the sealing and cold-duty polymer, PP is the stiffness and clarity polymer, PA is the barrier and toughness polymer that cannot seal itself. Most commercial structures combine two of them for exactly that reason.
Polyethylene: the default for freezer duty
Polyethylene remains flexible far below the temperatures used in frozen storage, which is the single most important property for a bag that will be handled, stacked and dropped at minus eighteen degrees or lower. Low density and linear low density grades are the usual choices, with the linear low density material contributing puncture resistance and seal strength. A polyethylene bag is the reference primary pack for IQF fruit and vegetables precisely because it does not become brittle in the cold store.
Polyethylene is a good water vapour barrier and a poor oxygen barrier. For a frozen product with a twenty-four month shelf life this is often acceptable, because the dominant deterioration mechanism at minus eighteen degrees is moisture migration and glaze loss rather than oxidation. For a product with fat that oxidises, a nut kernel or a fatty seed, oxygen ingress through a single polyethylene web becomes the limiting factor and the structure has to change.
The seal is where polyethylene earns its place. It seals to itself over a wide temperature window, which tolerates line variation, and it seals through light contamination better than most alternatives. On a vertical form fill seal line running dusty product, that tolerance is the difference between a two per cent reject rate and a ten per cent one.
Polypropylene: stiffness, clarity and heat
Polypropylene is stiffer, clearer and more heat resistant than polyethylene. Cast polypropylene is used where a soft clear film with a reasonable seal is wanted, and biaxially oriented polypropylene is used as a printed outer web where stiffness, gloss and dimensional stability matter. In a retail dried fruit pouch, the outer web is very often biaxially oriented polypropylene and the inner seal layer is polyethylene.
The weakness is cold. Polypropylene has a glass transition well above the temperatures used in frozen storage, and unmodified grades embrittle. A polypropylene-dominant structure that survives a laboratory drop test at room temperature can crack along a fold after a week in a blast-frozen pallet. If a converter proposes a polypropylene structure for a frozen line, ask for cold drop data at the actual storage temperature rather than at ambient, and ask for it after conditioning rather than immediately out of the freezer.
Where polypropylene is clearly correct is in ambient dried goods, in packs that will be filled warm, and anywhere the pack has to stand up on a shelf without a rigid outer.
Polyamide: barrier and toughness, at a cost
Polyamide provides a genuinely different oxygen barrier and a step change in puncture resistance. It is the layer that stops a sharp frozen fragment, a stalk or a shell edge from perforating the pack during palletisation and transport. For vacuum packs and for thermoformed packs it is close to unavoidable.
Two limitations matter commercially. Polyamide is hygroscopic, so its barrier degrades as it takes up moisture, which is why it is almost always placed as a middle layer protected by polyethylene on the food side. And it does not seal to itself usefully, so it is never a standalone web in a food bag.
Where a very high oxygen barrier is required, ethylene vinyl alcohol copolymer is used instead of or alongside polyamide, again as a protected middle layer, because it is even more moisture sensitive. A specification that says nylon barrier without saying which layer carries the barrier and how thick it is has not specified anything.
Why the real answer is a laminate
Because the three polymers are good at different things, most working structures are laminates, a point that also shapes the flexible packaging category as a whole. Three common ones:
- PE monoweb. Bulk liner and freezer bag for IQF fruit and vegetables, often as the inner web of a bulk pack. Cheapest, most cold-tolerant, weakest oxygen barrier.
- PA/PE. Vacuum and heavy-duty packs. Polyamide outside for toughness and oxygen barrier, polyethylene inside for the seal and food contact.
- BOPP/PE or PET/PE. Printed retail pouches and tray lidding. Stiff printable outer, polyethylene seal layer.
Each added layer buys a property and costs recyclability, thickness and money. The discipline is to write the requirement rather than the structure: state the required oxygen transmission rate, the water vapour transmission rate, the seal strength, the cold drop performance and the shelf life to be achieved, and let the converter propose a structure that meets them. Then verify the proposal rather than accepting the datasheet, because datasheet values are measured on the film and not on the finished seal.
What the packaging regulation changed
Regulation (EU) 2025/40 on packaging and packaging waste applies generally from August 2026 and replaces the earlier packaging directive. Two of its mechanisms bear directly on the choice between these polymers.
The first is design for recycling. From the start of 2030 packaging placed on the Union market has to be recyclable, assessed against design-for-recycling criteria and graded on a performance scale, with packaging below the defined threshold no longer permitted. Multi-material laminates are the structures most exposed to this, because a polyamide or aluminium layer in a polyolefin web is what pushes a pack out of an existing recycling stream. Mono-material polyethylene structures, where stiffness and barrier are achieved by orientation and coating rather than by a different polymer, exist for exactly this reason and are worth asking about now rather than in 2029.
The second is minimised packaging. The regulation restricts empty space in grouped, transport and e-commerce packaging and requires packaging to be reduced to the minimum necessary for functionality and safety. Overspecified film thickness carried forward from an old drawing is not just a cost line, it becomes a compliance question that the person placing the packaging on the market has to be able to answer with documentation.
The regulation also restricts per- and polyfluoroalkyl substances in food contact packaging above defined thresholds. Where a barrier or release coating has historically relied on fluorinated chemistry, particularly on fibre-based packaging, that route is closing and the supplier should be asked to confirm the position in writing.
The paperwork does not change with the polymer
Whatever structure is chosen, the documentary obligations are the same and they are set out in the food contact materials guide. For plastic layers, Commission Regulation (EU) No 10/2011 requires a written declaration of compliance at every stage of marketing up to but excluding retail, and it has to cover the actual structure supplied, the food types it is intended for, and the time and temperature conditions of use. A declaration written for ambient dry food does not cover a frozen wet fruit application, and a declaration for the seal layer alone does not cover the laminate.
Good manufacturing practice for food contact materials, under Commission Regulation (EC) No 2023/2006, applies to the converter as well as the resin producer. Printing inks on the reverse of a reel that will be wound against the food contact face are a recurring finding, and the converter should be able to describe how set-off is controlled.
How to run the decision
- State the storage temperature and the handling profile, including whether the pack is dropped, palletised loose or cased.
- State the shelf life and the deterioration mechanism you are protecting against: moisture, oxygen, light or physical damage.
- Derive the required barrier from that mechanism rather than copying a competitor structure.
- Ask for cold performance data at the real storage temperature, not at ambient.
- Ask the converter for the declaration of compliance for the exact structure, in writing, before the first order.
- Ask how the structure is graded for recyclability under the packaging regulation, and what the mono-material alternative would cost in performance.
- Run a shelf-life trial in the proposed structure rather than in a laboratory pouch.
Steps four, five and seven are the ones most often skipped, and they are the three that produce claims.
Where the comparison is usually got wrong
Specifying by thickness is the first error. Fifty microns of polyethylene and fifty microns of a polyamide laminate are different products with different costs and different failure modes, and a purchase order that says fifty micron bag invites substitution.
Testing at the wrong temperature is the second. A film qualified at ambient tells you very little about what happens at minus twenty-five degrees in a full pallet under compression.
Assuming the barrier survives conversion is the third. Seal areas, gussets and perforations are where oxygen actually enters, and film-level transmission rates measured on a flat sheet do not capture that. Where shelf life depends on the barrier, measure the finished pack.
Vorezan’s position
Vorezan is an information platform. We do not sell packaging, convert film, or certify structures, and nothing here is a recommendation to use a particular material for a particular product. Polymer behaviour varies by grade, by converter and by application, and regulatory positions change. Confirm the current text of Regulation (EU) 2025/40, Regulation (EU) No 10/2011 and Regulation (EC) No 2023/2006 in the Official Journal, and obtain structure-specific declarations and test data from your supplier before committing a specification.
