Music Division Skip navigational links. The lifespan of a plastic is largely determined at the manufacturing stage. Variables such as basic resin, the materials added to the basic resin to alter its properties, the lamination of materials with dissimilar properties, and the manufacturing process itself, all directly affect the lifespan of the plastic. Plastics can be divided into two main classes, thermoplastic and thermosetting.
Thermoplastics soften and flow when heated and are normally shaped by heat and pressure.
They will soften and flow again when re-heated. Vinyl, used in the manufacturing of LP's, is a thermoplastic. Thermosetting plastics are moulded under heat and pressure. A chemical reaction occurs so that once molded they do not soften when re-heated and will normally char before melting. Most 78s are made of thermosetting plastics.