Editing Polyethylene (section)

===Cross-linked (PEX or XLPE)===
{{Main|Cross-linked polyethylene}}
PEX is a medium- to high-density polyethylene containing [[cross-link]] bonds introduced into the polymer structure, changing the thermoplastic into a [[thermoset]]. The high-temperature properties of the polymer are improved, its flow is reduced, and its chemical resistance is enhanced. PEX is used in some potable-water plumbing systems because tubes made of the material can be expanded to fit over a metal nipple and it will slowly return to its original shape, forming a permanent, water-tight connection.