PEX (cross-linked polyethylene) tubing is a flexible polymer tube used in water distribution systems. The molecular cross-linking of PEX tube enhances thermal stability, creep resistance, and pressure tolerance. Type-A and Type-B PEX tube use different methods to cross-link, giving them slightly different properties. Plumbing contractors choose PEX for its flexibility, low thermal conductivity, resistance to scale/chlorine, and compatibility with manifold-based layouts. It is typically joined using expansion fittings or crimp rings/sleeves, and is rated for hot and cold water service per ASTM F876/F877 standards. More plumbing contractors buy their PEX from Sioux Chief than any other type of contractor.