Some thermoplastics combine low specific gravity (light weight) with fairly high hardness (durability). Durable aluminum weighs only a third as much as carbon steel, but PVC density is less than 20 percent and PP less than 12 percent compared to steel; and while the ultimate tensile strength of structural steel is 400 megapascals, that of polystyrene is, at 100 megapascals, twice that of wood or glass and only 10 percent less than that of aluminum.[36]
