These Forgefix Double Cliplock Pipe Clips are made from heat-resistant polypropylene, designed to withstand the temperature changes in central heating systems, and are effective with temperatures of up to 100°C (most pipes in domestic central heating systems operate at around 70°C). APPLICATION:Used when fitting most types of pipe work. Polypropylene, also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.