PEX-Aluminum-PEX, or PEX-AL-PEX, is PEX tubing with an embedded layer of aluminum. The aluminum serves as an oxygen barrier and keeps the tubing rigid. PEX-AL-PEX offers the additional advantages of less linear expansion and a larger diameter than standard PEX.
Due to the tubing’s different dimensions and aluminum layer, few options exist for fittings with PEX-AL-PEX. Standard PEX-Aluminum-PEX (i.e. the Uponor MLC MultiCor and Rifeng PEX-AL-PEX available on PexSupply.com) only works with compression fittings designed PEX-AL-PEX and Uponor’s MLC press fittings. PEX-AL-PEX compression fittings generally have male threads opposite the compression end, and must be connected to additional pieces in order to create couplings, elbows, tees, etc. MLC fittings require a costly tool and may not be a viable choice for small projects. Make sure to use a chamfering tool to prep PEX-AL-PEX prior to making a connection with either of these methods. Doing this creates a beveled edge on the inside of the tubing, which allows the o-ring to set properly.
Viega’s FostaPEX PEX-AL-PEX is not sized the same as standard PEX-AL-PEX. FostaPEX only works with Viega’s PEX Press fitting system. PEX Press fittings are also compatible with standard PEX tubing, but not standard PEX-AL-PEX. FostaPEX has its own prep tool, which peels the outer layer before the fitting connection can be made.