are films made of several layers. A classic, three-layer multilayer for bags contains, for example, a contact layer that guarantees an inert surface, the layer for gas/steam barrier that inhibits the diffusion of gases and aerosols, and the outer layer that increases the stability of the material. A binding layer is included in between the three layers which holds the layers together by physio-chemical interaction. The contact layer must be weldable, flexible, chemically and mechanically resistant and may not emit extractables or leachables. See bags and bag materials.