For water lines, there are three grades: PEX-A, PEX-B and PEX-C. They’re manufactured differently, PEX-A being slightly more flexible. If you’re ordering online, go ahead and spend a few cents extra for PEX-A. But don’t go running around town looking for it; the difference isn’t that big. The plumbers we talked to would be willing to use any of the three types in their own homes. PEX is also popular for in-floor radiant heating systems, for which you need PEX tubing with an oxygen barrier.
