Polypropylene is a thermoplastic "addition polymer" made from a combination of propylene monomers. It is among the cheapest plastics available, has the lowest density of commodity plastics, and is one of the top three most used polymers today. Polypropylene offers high flexural strength, a low moisture absortion rate, chemical resistance, impact strength, and fatigue resistance. Its typically used in packaging containers, fender liners, instumental panels, medical vials, petri dishes, along with acid and chemical tanks.