AO Smith® produces water heater dip tubes with cross-linked polyethylene (PEX), polypropylene and polysulfone polymers. PEX is the primary material that is utilized for most of our dip tubes and we have been manufacturing PEX dip tubes since 1996. PEX is a polymer that is produced by cross-linking high density polyethylene molecules, creating a thermoset matrix that provides excellent long-term performance in the hot chlorinated water environment of a water heater.