Polypropylene (PP) is the commodity thermoplastic with the lowest density. With lower density, parts are molded with lower weight. Other typical properties of Polypropylene is that it is tough and flexible, especially when copolymerized with ethylene. This allows polypropylene compounds to be used as an engineering thermoplastic, competing with materials such as acrylonitrile butadiene styrene (ABS). Polypropylene is at room temperature resistant to fats and almost all organic solvents, apart from strong oxidants. Non-oxidizing acids and bases can be stored in containers made of PP. Polypropylene is recyclable and has the number “5” as its resin identification code.