Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging and labeling, textiles, stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, transvaginal mesh and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.

A semi-crystalline, white, semi-opaque commodity thermoplastic made in a very wide variety of grades and modifications. It is a linear polyolefin which can be compared in many ways to high density polyethylene (HDPE) and that is manufactured in a very similar way. The catalysts used control the polymer's stereoregularity quite well so that commercial polypropylenes (PP) are usually predominantly isotactic. 

PP homopolymer is harder and has a higher temperature resistance than HDPE but lower impact resistance and becomes brittle below ~0C. Hence copolymer grades are preferred for all applications exposed to cold/winter conditions. These copolymers have better impact strength, maintained down to lower temperatures, than homopolymer at the expense of quite small reductions in other properties. Like polyethylenes, PP has good chemical but poor UV resistance (unless stabilised or protected).

Due to thermal stability issues with materials such as PP, additives such as anti-oxidants are invariably used during processing. It should also be noted that when considering the use of heat sealable films, that this product is in fact a coextruded film, comprising a PP core layer and PP/PE copolymer outer layers. These films are also corona treated to aid adhesion and may well also contain an anti-blocking additive such as silica. 

Applications include (for homopolymers) appliance housings, housewares, packaging, cassette holders and fibres, monofilaments and slit-film tapes; for copolymers pipes, containers, boat hulls, seat shells and automotive parts e.g. battery cases and bumpers though the latter are often made from more heavily elastomer-modified polypropylenes.