Metallizing of PET sheet under vacuum conditions is a proven technology to achieve special optical properties or a metal look for decorative applications and as mentioned above to reduce the diffusion of gases and flavors through the film. The most commonly used metal is aluminum but other metals can also be used.
Metallised films have a reflective silvery surface similar to aluminium foil and are highly flammable. The coating also reduces the permeability of the film to light, water and oxygen. The properties of the film remain, such as higher toughness, the ability to be heat sealed, and a lower density at a lower cost than an aluminium foil.
This gives metallised films some advantages over aluminium foil and aluminium foil laminates. It was thought that metallised films would become a replacement for aluminium foil laminates, but current films still cannot match the barrier properties of foil. Some very high barrier metallised films are available using EVOH, but are not yet cost effective against foil laminates.
