Flat material made of any substance which, unlike a sheet, is so thin that it is limp. Also referred to as ‘foil’, which is derived from the Latin term "folio" for 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. Roll-fed material such as film can be treated by means of atmospheric pressure plasma (PlasmaBeam) or in a low-pressure plasma using the roll-to-roll system.