Used in textiles, they are made from various raw materials. Those derived from petroleum, coal, and natural gas include polyesters, acrylics, nylon, polyethylene, polypropylene, polyvinylchloride, polyurethane, and synthetic rubbers. Fibres derived from cellulose include rayon, acetate, and triacetate. Inorganic fibres include glass and metal. Synthetic fibres such as nylon are produced by extruding the molten thermoplastic through extrusion dies called spinnerets into air that cools the fibres. The most widely used polyester fibre is PET (polyethylene terephthalate), which is used in carpeting.