Polypropylene (PP) is thermoplastic polyolefin. It can be formulated as a homopolymer (PPH) or a copolymer (PPC). Copolymers are more flexible that homopolymers and can reach up to high impact ratings including No Break. Polypropylene is a little harder than ethylene. Its natural color is a milky white, but clarifiers can be added to reach very good levels of clarity. Wikipedia Link