Thin aluminum foil is not particularly strong and it is frequently laminated to stronger material to reinforce it. The cheapest reinforcing material is paper and laminates of foil and paper are widely used in packaging. For foil gauges below about 0.0007 inch, the strength of the laminate is almost entirely due to the reinforcing paper on film. However, the barrier properties are dependent largely on the foil. The film normally used for reinforcing foil is regenerated cellulose, cellulose acetate, polyester, polyamide and polypropylene. These films, in addition to providing strength, protect the foil against mechanical damage. They also block any perforations in the foil. Lamination of foil to paper is usually done by wet bonding, where the two webs are combined with an adhesive in the wet state and drying takes place through the paper web.
Lamination of film to foil is normally done by dry bonding, where the wet adhesive is applied to one web, dried out and then the other web is brought into contact with the adhesive coated surface, and the combination passed through nip rolls which may be heated. A third method of laminating is by hot melts, where the adhesive is applied in a heated molten state to one web, which is then combined with the other web, followed by chilling to set the adhesive. No drying is necessary, since there is no volatile liquid to remove. Extrusion lamination which in principle is a variant of hot melt lamination, is done by extruding a film of molten plastic such as polyethylene through a flat die, bringing the foil and paper or film together with the extruded polyethylene film sandwiched in between, and nipping the combination between rolls chilled to solidity the molten plastics.