Dense gaskets shall normally be black extrusions with a Shore A hardness of 70 +5/-4 for hollow profiles and 60 +5/-4 for solid profiles, and conforming to ASTM C864 or BS 4255-1. Outdoor and indoor gaskets shall be silicone, EPDM, neoprene or a Thermal Plastic Elastomer (TPE). However TPE gaskets are not permitted to be used where their performance is dependent upon compression resistance. Where the colour of the gasket is other than black, only heat cured silicone rubber is to be used