Barrels can be constructed of plastic, laminated paperboard or steel. Folding cartons made of paperboard or molded pulp can also be of a clamshell shape. Linerboards are test liners (recycled paper) or kraft paperboard (of various grades). Cellulose is mainly used to produce paperboard and paper. In Sweden, Tetra Pak launched tetrahedral paperboard cartons in 1952. Packaging with perforations in paperboard or plastic film is easy for consumers to open. Many cartons are made out of a single piece of paperboard. Sandwiches are packaged in paperboard rather than sealed plastic. In 1817, the first paperboard carton was produced in England. Drums can also be made of durable plastic or paperboard. Before 1925, tennis balls were packaged in wrapped paper and paperboard boxes. The peak is typically stiffened by a sewn-in piece of paperboard or stiff plastic. These are called top Fourdriniers and they make multi-ply paper or paperboard. The paper and paperboard industry is quite energy and capital intensive. Each page panel is a minimum of two plies of paperboard thickness.