Metallised PET is polyester film with a few nanometres of aluminium; aluminium foil is solid metal, 6 µm and up. Film is lighter, cheaper and tears less; foil is a true vapour barrier and survives heat that would melt film. Buyers often ask for one when they mean the other, so here is how they differ and when each is the right call.
What each one is
Metallised PET is polyester film with an extremely thin layer of aluminium deposited on it in a vacuum chamber. The aluminium layer is a small fraction of a micron thick; the film is what you are actually handling. It is often called mylar film after an old trade name.
Aluminium foil laminate is solid rolled aluminium foil, typically several microns thick, bonded to a carrier such as polyethylene, polyester, woven scrim or kraft paper. The foil is a real metal layer; the carrier stops it tearing.
Side by side
The table gives the general shape of the difference; the figures for any particular roll come from its own data sheet.
| Metallised PET (VMPET) | Aluminium foil laminate | |
|---|---|---|
| Aluminium layer | Vacuum-deposited, a fraction of a micron | Solid rolled foil, typically 6–12 µm |
| Weight and cost | Low | Higher |
| Flexibility | Folds and creases without cracking | Foil can crack at sharp folds; carrier limits this |
| Visible reflectivity | High, mirror or matte, can be embossed | High, plain metallic |
| Emissivity | Higher than foil | Lower; better radiant-heat performance |
| Moisture and oxygen barrier | Good | Near-total |
| Heat tolerance | Limited by the PET and the metal layer | Limited by the carrier, foil itself unaffected |
| Printability | PET side prints and accepts adhesives | Depends on carrier |
Sources for the general properties: Wikipedia, “Metallised film”; TAPPI, “An economic value model for converters” (2007). Figures for any specific construction come from its data sheet.
Where metallised film wins
- Cost and weight. Far less aluminium, so cheaper and lighter per square metre.
- Flexibility. Folds and creases without cracking, which suits tents, liners and anything that is packed flat.
- Appearance. Can be made mirror-bright or matte, embossed with a pattern, and metallised on both sides.
- Printability. The polyester back accepts printing and adhesives cleanly.
Where foil laminate wins
- Emissivity. Solid foil has a lower emissivity than a metallised surface, which means it reflects a higher share of radiant heat. For insulation that is the number that matters.
- Durability of the reflective layer. A metallised layer can abrade or oxidise over years; solid foil is more robust, especially outdoors or on a roof.
- Barrier. Foil is a near-perfect barrier to water vapour and oxygen. Metallised film is good, foil is better, which is why food and pharmaceutical packaging uses foil.
- Temperature. Foil on a polyester or scrim carrier tolerates heat that would damage a metallised film’s coating.
How to choose
The most common mistake we see is a request for “foil” from a buyer who has a metallised film in hand, or the reverse, because both look silver on a roll. The quick test is weight and a fold: metallised film is light and creases cleanly; foil laminate is heavier and a sharp fold leaves a permanent line in the metal. Settle which one you have before comparing quotes, or the quotes will not be for the same thing.
If the material’s job is to reflect light evenly, be folded and look good, choose metallised film. If its job is to reflect heat for years, block moisture or survive high temperature, choose a foil laminate. Many finished products use both: a metallised film face for appearance and a foil layer inside for barrier or emissivity.
We supply both and can laminate either to scrim, foam, bubble or paper. The unbacked foil side of the comparison is Aluminum Foil, Plain; the metallised side is the Grid Reflective Film, Silver and the rest of that family. Describe the end use and we will recommend the construction and send swatches of each.