When you walk down the plumbing supply aisle these days, you'll find the majority of tubes are made from flexible plastic—most notably PEX (cross-linked polyethylene). This pipe is gaining popularity for its ease of installation and low cost. It's also less prone to cracking from freezing and thawing than copper.
There are three different types of PEX: PEX-A, PEX-B and PEX-C. The letters indicate the manufacturing method and do not affect performance ratings. PEX-A is the most common type used in homes and offers a superior resistance to long-term oxidation. PEX-B is stiffer than PEX-A, but it still installs easily. It's less expensive than PEX-A and has the same resistance to cracking from freezing as PEX-A. It's also less prone to kinking and has an improved resistance to chlorine.
It's important to use only PEX tubing and fittings by the same manufacturer to avoid problems like mismatched parts that can create leaks and void warranties. It's also crucial to properly install PEX, following manufacturer instructions and industry standards to ensure a trouble-free installation.
For example, it's recommended to install manifolds at the water heater and then run short "home runs" of one-half inch hot and cold tubing to each fixture. This reduces potential leak points and simplifies plumbing by eliminating the need for tees and other fittings between the manifold and each fixture. You'll also want to install support tubes every 16 to 24 inches to reduce sagging and potentially harmful stresses on the tube.