That’s why there is no point in putting an EVOH oxygen barrier layer on the outside of a pipe where it is susceptible to Physical, Chemical & UV damage not allowing it to act effectively as an oxygen barrier at all. EVOH is a excellent oxygen permeation barrier but is a delicate material which needs to be protected within the pipe wall to maintain its integrity for the life of the heating system. With IVAR-PEX you can be confident that the oxygen barrier will protect your heating system from oxygen ingress.