Crosslinked polyethylene tubing, also known as PEX, is a flexible water supply piping system that is ideal for replacing copper water lines. Common colors are red for hot water and blue for cold. It comes in either pre-cut lengths or in big rolls on spools. PEX is so flexible it can make 90 degree bends without elbow fittings, and its availability by the roll means fewer coupling are needed, as well. There is a large range of fittings available, designed to connect to existing water lines, including snap-on fittings. There are also manifolds to centralize the distribution of water lines.