PET, foil, polyethylene: how the layers in a laminate decide shelf life
No single film prints well, blocks air and seals cleanly. A laminate gives each job to a different layer, and the choice of layers decides how long your product keeps.
Pick up almost any printed pouch and you are holding two or three films bonded into one sheet. It looks like a single material, but each layer is there for a different reason, and choosing them is the most important decision in a packaging job.
Why one film is not enough
A pack has to do three things: carry the print, protect the product and seal shut. No single plastic does all three well. Polyester prints beautifully but will not heat seal to itself. Polyethylene seals easily but stretches on the press and lets oxygen through. Aluminium foil blocks almost everything but tears and cannot be sealed at all. Lamination puts the three together so each one covers for the others.
The three jobs
- The outer layer carries the print. This is usually PET or BOPP: stiff, clear and stable under heat. The ink is printed on the inside face, so it ends up sandwiched between layers and cannot scuff or touch the product.
- The middle layer is the barrier. Aluminium foil, metallised PET or nylon sits here to keep out oxygen, moisture and light. Packs for products that are not sensitive can leave this layer out.
- The inner layer makes the seal. Polyethylene or cast polypropylene melts at a lower temperature than the outer layers, so the sealing jaws can weld the pouch shut without damaging the print. It is also the layer that touches the product.
Common structures and where they are used
| Structure | What it gives you | Typical use |
|---|---|---|
| BOPP / LDPE | Clarity and economy | Bakery, stationery, dry goods with a short shelf life |
| PET / LDPE | Stiffness and good print | Pulses, flours, general grocery |
| PET / met PET / LDPE | Light and moisture barrier | Snacks, namkeen, spices |
| PET / foil / LDPE | The highest barrier | Coffee, pharma powders, products with a long shelf life |
| Nylon / LDPE | Puncture resistance | Vacuum packs, frozen food, liquids |
What to tell your converter
You do not need to specify the structure yourself. Tell us what the product is, the fill weight, the shelf life you are aiming for, how the pack will be filled and how it will be stored and sold. From that we can propose a laminate and explain what each layer is doing in it.
Have a product to pack?
Tell us what it is and how it is sold. We will reply with a laminate, a format and a price.
