Thermoplastics are a subset of plastics that can be re-shaped with the application of pressure and heat multiple times. Different types of thermoplastics have additional properties that make them especially well-suited to different jobs, but all thermoplastics share the same characteristic of flexibility when exposed to heat and force.
Thermoplastics are also known as thermosoftening plastics because they become malleable when heated. Although they are pliable above a certain heat threshold, they return to a solid once they have been sufficiently cooled. This is a contrast to most other types of plastic, which are unable to return to a solid state after they have been heated beyond a certain point. For this reason, thermoplastics are put to unique uses in a number of manufacturing and engineering industries.
Apart from their primary characteristics, thermoplastics vary slightly in usage and properties. For example, polystyrene is a hard, water-resistant thermoplastic, according to BBC. This makes it an excellent choice for creating toy models and for packaging that will not be exposed to extreme heat sources in transit. Polymethyl methacrylate is also a stiff thermoplastic, but it is also an electrical insulator and can be polished well, so it is often used in vehicle windows and light covers.