Polypropylene (or polypropene, abbreviated as PP) is a thermoplastic polymer which can vary in tacticity. The most interesting product from the commercial point of view is the isotactic one: it is a semi-crystalline polymer characterised by a high breaking point, a low density, and a good heat and abrasion resistance.
The density of isotactic polypropylene is 900 kg/m³ and the melting point is often above 165°C. The chemical properties, determined in the production phase, include stereoregularity, molecular mass and the polydispersion index. The atactic product, instead, is like a rubbery material, and is of little commercial interest (it has only been used as an additive).
It is one of the most widely used thermoplastics in the automotive, packaging, telecommunications, gardening and telephony sectors, among others.