Pex-al-pex or “FostaPEX” The aluminum layer laminated on the standard pex-b tubing serves a couple purposes. First, it helps stabilize the pex and limits the expansion and contraction with changes in fluid temperatures. This makes it somewhat similar to copper pipe for certain application in heating or hot water systems. Another benefit is the aluminum provides a barrier to oxygen diffusion. This is needed for closed hydronic heating systems. The aluminum also helps keep the pipe in shape wherev