Thermoplastics can be welded using a range of methods. The basic principle is that the plastic is reheated to its melting temperature and a joint is then formed between the plastic structures. Typically, plastic welding methods are used to join plastic pipes, with the main techniques including hot plate welding, electrofusion welding and contact welding. Plastic sheets and films can also be welded using a range of methods. The main welding methods for plastic sheets are hot plate welding, hot gas welding and extrusion welding.