Polypropylene is from the same family of polymers as polyethylenes, giving it very similar characteristics. Both are resistant to water. The biggest difference between the two is their relative density, where P/P is around 0.90 and P/E is .940 to .965. Polypropylene also has a higher service temperature and is more rigid and resistant to environmental stress cracking. Polypropylene can be difficult to bond, has poor weatherability and is normally flammable. Its properties can be enhanced by adding a variety of fillers such as glass, talc or a flame retardant. •  Homopolymer P/P is typically found in fibers, filaments and packaging film due to its water barrier characteristics. •  Random copolymer P/P is tougher and more impact resistant due to a flexible ethylene component added to its molecular structure. These are usually found in interior or exterior automotive trim pieces and parts for furniture.