Why Multilayer Packaging Is Harder to Clear for Food Contact

Multilayer and multi-material packaging covers a wide range of structures:

• Laminates, where separate films or foils are bonded with adhesive

• Co-extruded films, where several polymer layers are produced together

• Coated structures, where paper, board or film carries a coating or barrier layer

• Combinations of materials, such as plastic with paper or aluminium

Each type has its own considerations, but they share a common problem: the compliance of the finished pack depends on many parts and how they interact.

A single-material pack often has one main supplier and one main declaration. A multilayer pack may have a film supplier, an adhesive supplier, an ink supplier, a coating supplier and a converter who puts it all together.

Each of them can say their own product is compliant, and each statement typically covers only their part. Nobody necessarily takes responsibility for the finished structure unless someone assembles the pieces. Our article onwhat a declaration of compliance should contain explains how to judge any single declaration, but with multilayers you need to judge how the declarations fit together.

It's tempting to assume that if every layer is individually compliant, the pack is too. That doesn't automatically follow.

• The conditions of use may differ: a layer approved for one temperature or food type may sit in a structure used under different conditions.

• Processing can change materials. Heat during lamination, forming or sealing can alter what's in a layer.

• Layers interact. Substances can move between layers during storage, not just into the food.

The finished structure, as it's actually made and used, is what needs to be assessed.

One of the most important and most misunderstood ideas in multilayer compliance is the functional barrier. The idea is that a layer positioned between the food and another layer can prevent substances in the outer layer from reaching the food, so those substances may be treated differently from ones in direct contact.

It's a useful concept, and several regulatory systems recognize it in some form. But it isn't automatic:

• It must actually work. The barrier has to be effective for the substances involved, under the real conditions of use.

• It depends on conditions. Heat, time and the type of food can all affect whether a barrier holds up.

• Damage matters. Cracks, pinholes or seal areas can undermine it.

• It isn't universal. The conditions under which regulators accept this approach differ between markets and between types of substance.

A claim that a layer is a functional barrier needs evidence for the specific structure and use. It's a judgment to demonstrate, not a box to tick.

In a multilayer structure, the components that people think about least are often the ones that cause the most trouble.

Adhesives hold layers together and may release residues or form by-products as they cure and age. Some adhesive chemistries need specific attention.

Printing inks are frequently applied to the outside, but if the printed surface touches the inside of the pack when it's reeled or stacked, ink components can transfer to the food-contact side. This is known as set-off, and it's a classic, easily overlooked route to food contact.

Coatings and lacquers add further layers of substances to account for.

All of these sit alongside the polymers that people usually think of first, and they often come with less documentation.

Testing a single material is relatively straightforward. Testing a multilayer is not.

• Which layer is being tested? And which one actually touches the food?

• Are you testing the finished structure, as made and used, or individual components?

• Do test conditions match real use in terms of food type, temperature and time?

• Is the sample representative, given that structures can vary across a roll or between production runs?

Test results are only meaningful if the sample and conditions reflect the real pack.

Different regions approach multilayer structures in different ways. Some have specific provisions addressing layered materials, such as how substances behind a barrier are treated. Others take a more general approach based on whether any substance is expected to migrate into food. Labelling and documentation expectations also differ.

For a company selling in several markets, the same structure may need different evidence to show compliance in each one. That's why understanding how major systems differ matters so much, and it's one of the biggest practical challenges for multi-market teams.

Multilayer structures are often hard to recycle because their layers are bonded together and made of different materials. As recyclability rules and producer responsibility costs grow, many companies are looking at simplifying structures or moving toward fewer materials.

That creates a tension: the barrier performance that protects food may depend on those multiple layers, and any redesign needs a fresh compliance and shelf-life assessment. We explain the regulatory background in our guide toextended producer responsibility for packaging. The key point is that a more recyclable design isn't automatically a compliant one.

1. Map the structure. List every layer and component, the supplier of each and the role it plays, including adhesives, inks and coatings.

2. Identify what touches the food. Pinpoint the food-contact layer and any layers you're treating as barriers.

3. Collect documentation layer by layer. Get declarations and supporting information for each component, and check that each one covers your conditions of use.

4. Check regulatory status per market. Confirm each substance is acceptable in every market you sell into.

5. Evaluate any barrier claim. Gather evidence that the barrier works for the substances and conditions in question.

6. Test the finished structure. Use conditions that reflect real use, and make sure samples are representative.

7. Consider unintended substances. Include a reasoned assessment of impurities and by-products.

8. Build a structure-level file. Pull everything together so the whole, not just the parts, is documented.

9. Control change. Require a compliance review for any change to any layer, supplier or process.

• Which markets and conditions of use does your declaration cover?

• Have impurities, by-products and breakdown products been considered?

• What do you know about how your product behaves in laminated or coated structures?

• Will you tell us about changes to formulation or process?

• Can you provide the information needed to assess the structure as a whole?

Assuming layer-by-layer compliance equals pack compliance. The whole structure needs assessing.

Treating "functional barrier" as a label. It needs evidence.

Forgetting inks, adhesives and coatings. They're frequent sources of issues.

Ignoring set-off. Transfer from the printed surface is easy to miss.

Testing the wrong thing. Make sure tests reflect the real structure and use.

Changing one layer without review. The effects can reach the whole pack.

Multilayer packaging is hard to clear, but not impossible. The teams that handle it well treat the structure as one system, ask the right questions of each supplier and keep clear records. That discipline saves time and avoids unpleasant surprises in customer reviews and audits.

Understand how multilayer structures are designed, how migration is evaluated and how major markets regulate them in ourIntroduction to Global Regulations for Multilayers and Multi-Materials course.