Most mats are made of PVC rubber nitrile foam. Also used as a stabilizer in the manufacture of polyurethane foam. Polystyrene foams are produced using blowing agents that form bubbles and expand the foam. They were produced as molds to cast the whole body in foam rubber latex. Casper mattresses consist of four types of foam, memory foam, and polyurethane support foam. Most saddles include padding, generally foam or gel. Toy and replica versions made of polystyrene foam or plastic are also available. Wood makes a better support system for the newer memory foam and latex mattresses. EVA is one of the materials popularly known as "expanded rubber" or "foam rubber". Extruded polystyrene foam (XPS) consists of closed cells. The aircraft is made from aluminum sheet glued to Klegecell foam. The fluid can be gel, foam, or slickwater-based. The original "Windsurfer" board had a body made out of polyethylene filled with PVC foam. Since the development of gel memory foam, other materials have been added. Memory foam mattresses significantly decreased such events.