What is PEX-AL-PEX Tubing? Multi-layer PEX or PEX-AL-PEX, as the name implies, is a tubing where an aluminum core layer is sandwiched between 2 layers of PEX. This feature allows it to expand less at high temperatures and hold its shape better than regular PEX. The aluminum layers act as the Oxygen Barrier and can be used and certified for both Radiant Heating and Potable Water use. It is critical that this be used with approved PEX AL PEX connectors and fittings. Standard PEX fittings are NOT compatible with PEX AL PEX tubing.— Free Shipping to lower 48 States on all PEX Tubing. Exclude AK and HI