PEX piping is often referred to as cross-linked polyethylene, which is a type of plastic that has been chemically treated to resist stress cracking and degradation. The psi rating for PEX pipe varies depending on the thickness of the pipe wall - the thicker the pipe, the higher the rating. For example, thin-walled PEX tubing typically has a psi rating of 80, while thick-walled PEX tubing can have a psi rating of 100 or more.