Abstract: Multilayer composite plate in which a hard layer of a foamed plastics material, such as foamed polystyrene, is bonded between two outer layers, conveniently of plywood or chipboard. The composite plates may have peripheral slots formed by extending the outer layers beyond the edges of the intermediate layer to form flanges. The slots may be used to accommodate ties by which two composite plates abutted edge-to-edge are secured. Invention also concerned with method of bonding layers under partial vacuum and apparatus for performing the method.