PEX is cross-linked polyethylene tubing used for hot and cold water distribution and for hydronic radiant heat. It bends around corners instead of needing an elbow at every turn, tolerates freezing better than copper or CPVC, and joins with mechanical fittings rather than solder or solvent.
The three grades differ by how the cross-linking is done. PEX-A is the most flexible, has the strongest shape memory, and is the grade used with expansion (F1960) fittings. PEX-B is stiffer and less expensive and is joined with crimp (F1807) or clamp rings. PEX-C sits between them. All three carry the same pressure ratings and are interchangeable in a system as long as the fitting method matches the tubing.
Oxygen barrier PEX carries an EVOH layer that keeps oxygen from diffusing through the wall and corroding cast iron and steel components. Use it on any closed hydronic loop with a boiler, circulator or steel radiator. Non-barrier PEX is for potable water only.
Sizes are nominal, matching copper tube: 1/2" PEX has the same fitting size as 1/2" copper, though the inside diameter is smaller.
PEX tubing dimensions, pressure ratings and bend radius — full reference tables for every size from 1/4" to 2", including inside diameter and water volume per 100 ft.
