Multilayer Laminated Structures for Flexible Packaging

A multilayer laminated structure is a flexible packaging material built from two or more films bonded into one. Each layer is chosen for a job: print, stiffness, barrier or sealing. The finished laminate behaves as a single film on the packaging line. Almost every printed pouch and rollstock on a shelf is a multilayer laminate. The differences that matter are how the layers are built, what families they come from and what that means for the pack’s end of life.

This page is the construction manual of the materials section. It covers how duplex and triplex structures are put together, and how coextrusion and lamination divide the work of making layers. It covers what solventless lamination does differently from solvent-based bonding. And it covers why a multilayer pack can be perfectly recyclable or not recyclable at all, on one design decision. The structures themselves each have their own page here.

What multilayer means, and what it does not

Multilayer describes construction, not chemistry: a structure with more than one layer. That is the whole definition, and the distinction it is most often confused with is the one that actually decides a pack’s fate. Multimaterial describes chemistry: layers from different polymer families. The two are independent.

A BOPP/CPP duplex is multilayer and monomaterial: two layers, one family, fully at home in the polypropylene recycling stream. A PET/PE duplex is multilayer and multimaterial: two layers, two families, no clean stream. Same construction, opposite end of life, and the difference is not the number of layers but what they are made of.

Duplex and triplex: how structures are built

The construction vocabulary of laminated packaging is simple: a duplex laminate bonds two webs in one lamination pass, a triplex laminate bonds three webs in two passes. Each web enters the laminate as a finished film with its own properties, and the role assignment is consistent across the industry. The outer web carries print and stiffness. The inner web faces the product and seals. In a triplex the middle web exists to add a function the outer pair cannot deliver, almost always barrier.

The discipline of construction is subtraction, not addition. Every web adds material, cost, a lamination pass and complexity at end of life. So the question is never what can be added. It is what the least construction is that meets the requirement. Most products are duplex products. A triplex is specified when the barrier target exceeds what a coated or metallised duplex reaches. Coffee for long export chains and aggressive contents are the classic cases.

How layer thickness is written: microns, gauge and mil

A structure is quoted as a sequence of layers with a thickness against each one. The awkward part is that the same layer is written in different units depending on who is asking, and the units are not intuitive.

European specifications use microns, written µm. North American ones normally use gauge, and occasionally mil. These are not the same thing, and gauge is the one that catches people out: it is not a thousandth of an inch. One mil is a thousandth of an inch. One gauge is a hundredth of a mil.

12 microns and 48 gauge are the same film

The outer polyester web most often quoted as 12 µm in Europe is the same film an American specification calls 48 gauge. Forty-eight gauge is 0.48 mil, and 0.48 × 25.4 gives 12.19 µm. The two numbers describe one film, and a duplex written PET 12 / PE 50 in Brussels is written 48 ga PET / 2 mil PE in Chicago.

The total is not simply the sum, either. The adhesive between layers adds its own coat weight, so a laminate always measures slightly more than the films that went into it. That is why a structure is specified layer by layer rather than as a single overall figure. An overall thickness tells you what the pack feels like, not what it is made of.

Coextrusion and lamination: two ways to build layers

Layers enter a structure by two different routes, made at two different places in the supply chain. Coextrusion builds layers inside a single film as it is being made. At the film producer, several polymer melts flow through one die and solidify together into one web. Those layers cannot be separated. That is how a sealant film carries a slip layer on one face and a lamination-friendly surface on the other. It is also how an EVOH barrier layer sits buried in a core.

Lamination builds layers by bonding finished films together. At the converter, webs made independently, often on different technologies and by different producers, are joined with an adhesive into one structure.

Most structures use both

The two processes are complements, not competitors. A typical duplex is a laminate of two webs, and one or both of those webs is itself coextruded. The CPP sealant of a BOPP/CPP structure and the PE sealant of an MDO-PE/PE or PET/PE structure are almost always multilayer films in their own right. The film producer engineers them for sealing on one face and bonding on the other.

The division of labour is clean: coextrusion decides what each web is, lamination decides what the structure becomes.

Solventless lamination

Lamination processes differ in what carries the adhesive to the web. In solvent-based lamination the adhesive is dissolved in a solvent. That solvent has to be evaporated in drying tunnels before the webs meet. It costs energy, it demands solvent recovery, and it leaves the question of residual solvents in a food pack on the table.

In solventless lamination the adhesive is applied as it is. A two-component system is mixed and spread as a thin liquid film, with no solvent to remove. The webs are joined immediately, and the bond is built by chemical curing over the following days rather than by drying.

What the buyer actually feels

No solvent means no residual solvent risk in the finished laminate, and no retained-odour concerns over the product. That is why solventless has become the reference process for food packaging lamination. No drying tunnels means a shorter, more energy-efficient process.

The trade-offs are real but manageable. Solventless adhesives need their curing time before the laminate is slit and converted, and the process rewards clean, well-tensioned webs and disciplined adhesive metering. In practice the work is specification work. Match the adhesive system to the two surfaces being joined and to the duty the pack will face. Respect the curing window. Validate bond strength on the finished structure.

Adhesives and bond strength

The adhesive is the invisible layer of every laminate, and it is specified with the same care as the films it joins. Solventless systems are typically two-component polyurethane adhesives. The components are metered and mixed at the laminating machine and spread in a thin, uniform film. The bond then develops by chemical reaction over the days after lamination. During that window the laminate rests before slitting and converting. A bond that has not finished curing has not reached the strength the structure was designed around.

Bond strength is what holds the structure together through converting, filling, transport and retail handling. It is measured on the finished laminate as the force needed to peel the webs apart. The target depends on the duty. A light dry-goods pouch and a heavy pet food bag do not need the same bond.

Recyclability across multilayer laminated structures

Layers do not decide a pack’s end of life. Families do. A multilayer laminate whose webs all belong to one polymer family sorts and reprocesses in that family’s stream. A BOPP/CPP duplex and an MDO-PE/PE duplex both do. The lamination adhesive does not change that, at the thin levels design for recycling criteria account for. A laminate that combines families has no clean stream. PET over PE is one case, a triplex with an aluminium foil core the hardest. Conventional mechanical recycling does not separate what lamination has joined.

Where the alternative is not another laminate but a rigid container, the two formats reach recycling by different routes, and the comparison starts one level above the structure.

Keep the layers, change the families

This is why the industry’s design guidance reads as a construction instruction, CEFLEX in Europe and APR in North America among the bodies shaping it. Stiffness, printability and meaningful barrier once required a polyester or aluminium web. They are increasingly delivered inside one family instead: by oriented films such as MDO-PE, by coatings, and by thin functional layers used within the shares the criteria accept. Protocols such as RecyClass grade the results in classes from A to C.

The distinction that runs through this section holds here too: recyclable describes design, recycled describes outcomes, and both are settled per structure rather than per construction type. The regulatory frame, the PPWR timeline and what design for recycling requires in law, is covered in the flexible packaging sustainability section.

Typical structures and where they are covered

Every laminated structure in this section is a variation on the constructions above. Each family has its own page with the depth a specification discussion needs: barrier, sealing, food contact and applications.

The table read top to bottom is the design direction of the industry. The constructions stay. The families consolidate. Structures that once justified a foil core or a polyester web are being re-examined against what a single family can now deliver.

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