Did you know all plastics fall into only 2 categories when it comes to their reaction to heating? These 2 categories are called Thermoplastic and Thermosetting.
Thermoplastic materials become soft when they are heated and solid when cooled to room temperature. This is similar to heating and cooling wax. Thermoplastics are materials such as acrylics, cellulosics, polyamide, polystyrene, polyethylene, fluoroplastics, polyvinyls, polycarbonate, and polysulfone.
Thermosetting materials cannot be reheated and softened again. Once these are formed they cannot be reformed. This is simliar to baking a cake or boiling an egg. Thermosetting are materials such as aminos, casein, epoxies, phenolics, polyesters, silicones, and polyurethanes.