Flat material made of any substance which, unlike a sheet, is so thin that it is limp. From Latin "Folio" to be translated as leaf. Like sheets, metal foils are produced by rolling out a raw material block, while plastic foils are produced by extrusion and subsequent calendering. Similar to sheets, thicker films or foils are produced as flat foils, while thin films are produced as blow-extrusion films like a tube. Often, films require treatment with plasma, for example to prepare them for printing or coating or bonded (laminated) with other flat materials to form a multi-layer material. Film treatment can be carried out by atmospheric pressure plasma (PlasmaBeam) or in a low-pressure plasma using the roll-to-roll system.