PEX stands for cross-linked polyethylene. It is a poly plastic. PEX is a plastic tubing designed for potable (drinkable) systems that has been in the USA for several years. There are several brands of PEX on the market. For example – one brand has an one hundred year warranty, whereas another has a twenty five year warranty. Whatever the brand may be, PEX is a durable and solid material that is effective and efficient in the plumbing industry.