Multi-Layer Laminate Structures: How to Read and Choose PET/AL/PE and More
Walk through any snack aisle and the pouches look simple — but behind most of them is a carefully designed laminate structure, written as a stack-up like PET/AL/PE. Once you know how to read that shorthand, you can reason about cost, barrier and machine performance before you ever make a sample.
How to Read a Structure
A structure is written from the outside (print side) to the inside (sealant side), with layers separated by slashes. So PET/AL/PE means: a PET print layer on the outside, aluminum foil in the middle, and a PE sealant layer on the inside that contacts the product and forms the seal.
Classic Structures and Where They Are Used
| Structure | Typical Use | Why It Works |
|---|---|---|
| OPP/PE | Snacks, biscuits, candies | Low cost, good moisture barrier, clear |
| PET/PE | Soaps, liquids, dry goods | Stiff, printable, seals well |
| PET/AL/PE | Coffee, powder, high-barrier food | Full barrier to O₂, H₂O and light |
| PET/PA/PE | Frozen food, vacuum packs | Puncture-resistant, strong |
| PET/AL/CPP | Retort pouches | Heat-resistant seal, full barrier |
| PET/VMPET/PE | Snacks, confectionery | Metallic look, improved barrier, lighter than foil |
| PET/EVOH/PE | Transparent high-barrier food | Oxygen barrier with see-through clarity |
Choosing the Outer Layer
The outer layer carries the print and takes heat. PET is the default because it is stiff, clear and heat-resistant. OPP is chosen when cost matters most. When the pouch needs mechanical toughness — frozen food or sharp contents — PA (nylon) is added or substituted.
Choosing the Barrier Layer
The barrier sits between the outer and sealant layers. Aluminum foil is the strongest option and is required for light-sensitive products like coffee. Metallized PET gives a metallic finish with a lighter, cheaper structure. For transparent packages that still need oxygen protection, EVOH is the choice, always sandwiched between moisture barriers so humidity does not degrade it.
Choosing the Sealant Layer
The sealant must melt and fuse reliably in your sealing equipment. PE is the economical standard. CPP is used for retort applications and high-clarity pouches because it withstands higher temperatures. The sealant also determines the pouch's "mouth feel", flex-crack resistance and ease of opening.
Design Rules of Thumb
- Match the barrier to the product: don't pay for foil when a metallized film is enough.
- Consider the filling and sealing process: retort, hot-fill and vacuum all push the structure in different directions.
- Balance thickness: a slightly thicker sealant often prevents flex-cracking and seal failures better than a thicker barrier.
- Validate with real data: calculate the expected OTR/WVTR and confirm it meets your shelf-life target.
Get a Starting Point
If you know your product but not the structure, describe it to the ElagentPak Material Advisor. It recommends a laminate structure with performance and cost estimates, then you can verify the barrier with the Barrier Calculator.