Product Focus: Radiant Heating Systems Issue: 9/01 Qual-Pex is the newest addition to Weil-McLain's extensive line of radiant heating products. Qual-Pex is composed of two layers of cross-linked polyethylene joined with adhesives to a central layer of EVOH, which serves as an oxygen barrier from external conditions. The integrity of the oxygen barrier remains intact, even in heavy construction. Qual-Pex 1/2" tubing is rated ASTM F876/F877 and is available from Weil-McLain in 300-ft. and 1,000-ft. coils. Weil-McLain.