Forgefix pipe clip double cliplock forgefix pcdc22 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 100c most pipes in domestic central heating systems operate at around 70c 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 additio