Any of numerous synthetic materials that consist of giant molecules called polymers, with extremely long chains of repeating units derived from short molecules. Plastics can be formed into products by moulding or otherwise shaping. The two major divisions of plastics are the thermosetting resins and thermoplastic resins. Raw materials for plastics include coal and cellulose, but by far the chief source is petroleum. Because of their easy manipulation, economical manufacture, low specific gravity, and resistance to corrosion, plastics have replaced metal, wood, glass, and other materials in many applications. An immense array of plastic industrial and consumer goods is available.