A mattress is a large pad for supporting the reclining body, used as or on a bed. Mattresses may consist of a quilted or similarly fastened case, usually of heavy cloth, that contains hair, straw, cotton, foam rubber, etc., or a framework of metal springs, or they may be inflatable. Mattresses are usually placed on top of a bed base which may be solid, as in the case of a platform bed, or elastic, e.g. with an upholstered wood and wire box spring or a slatted foundation. Modern mattresses usually contain either an inner spring core or materials such as latex, viscoelastic or other flexible polyurethane foams. Mattresses may also be filled with air or water, or a variety of natural fibers, such as in futons. In Southeast Asia, bedding is made with kapok.