Polypropylene (PP) resins are thermoplastic polymers, meaning they may be formed with heat and re-melted without losing their intrinsic characteristics. Thermoplastics differ in this way from thermosets, which undergo permanent change after hardening. Thermoplastics are generally recyclable for this reason. Other thermoplastics include polyethylene, polyvinyl chloride, polystyrene, polycarbonate, acrylic, acrylonitrile，butadiene styrene, nylon, and polytetrafluoroethylene.