1. A classification for materials (textile fibers and resins) that can be made soft by the application of heat and hardened upon cooling.
2. Softening under heat and capable of being molded into shape with pressure, then hardening when cooled without undergoing chemical changes.
3. A polymer in which the molecules are held together by weak secondary bonding forces that can be softened and melted by heat, then shaped or formed before being allowed to solidify again.