A reusable putty designed to protect sensitive parts from heat damage during brazing, soldering and welding.
www.epicair.co.uk
Big ball of it on the pipe eg clump it on solder it / do your thing cool the joint with a wet towel and remove the paste/ compound as it will stat to transfer the heat back etc
Around 1980, I was working in ICI Seal Sands. The ICI project manager asked us test a new compound which insulated heat transfer along the pipe. He said he had obtained it from NASA. We were to stress relieve the joint on a joint between the pipe and a valve. It worked, absolutely incredable, today we would say space technology, and it was.