The ABC's of PEX Tubing

The ABC's of PEX Tubing

The ABC's of PEX Tubing

PEX tubing was invented in 1968 by a German scientist named Thomas Engle and introduced to the U.S. around 1980. The many benefits have made PEX tubing a popular choice for plumbing systems, such as affordability, flexibility, quick installation, and corrosion resistance. The most common residential PEX tubing construction sizes range from 1/2” to 1”. PEX tubing is rated up to 180°F at 100 PSI.


PEX stands for cross-linked polyethylene. Polyethylene is composed of chains of ethylene molecules referred to as polymers. These polymers don’t connect, which is what gives polyethylene its flexibility. Polyethylene is produced in two main forms: high density (HDPE) and low density (LDPE).


All PEX tubing is formed via extrusion, a process which subjects the HDPE to heat and pressure through a dye. The material must adhere to the same ASTM F876 and ASTM F877 standards, along with SDR9 dimensional standard for use in the United States. This would include the following criteria:

  • Pressure and temperature ratings
  • Minimum bending radius
  • Pipe wall thickness and Inside Diameter (ID)/Outside Diameter (OD) dimensions


PEX tubing is classified under three categories: A, B, and C. These letters aren’t grades as they are used to identify the manufacturing process and have nothing to do with quality or performance. Learn about how the different types of PEX compare to each other:



How is a PEX type chosen? For hot and cold water plumbing as well as for open-loop systems, both PEX-A and PEX-B are evident choices. However, PEX-B offers a more attractive combination of better health safety, higher durability, and lower price. For baseboards, radiators, radiant floor heating, snow melting, and other types of closed-loop heating systems, any PEX tubing type can be selected according to personal preferences or various comparison factors previously mentioned.


Additional factors influence the applications of each PEX type, such as the bending radius, pressure drop, and wall thickness. In addition, PEX tubing sizes are signified by CTS (copper tubing size), not OD (outside diameter) or ID (inside diameter). To dig deeper into the different types of PEX tubing and fittings, take the ‘PEX Tubing and Fittings’ AYU course, called our customer service department at 1-800-292-2737, or fill out a Contact Us form on