Lesson 1: How manufacturing methods make a difference

Most students in the U.S. and Canada are officially back in the classroom for the school year. But just because we’re no longer kids, doesn’t mean we can’t learn a little, too! During September, we’ll be going back to school with PEX. This week is lesson one.

What is PEX?

PEX is an acronym for crosslinked polyethylene. Crosslinked = X and polyethylene = PE. Because XPE doesn’t roll off the tongue quiet as nicely, we call it PEX. But what is polyethylene? It's a tough, light, flexible synthetic resin made by polymerizing ethylene. And when that resin is crosslinked through ~science~, it becomes even stronger.

The tubing is used for PEX plumbing, radiant heating/cooling, hydronic piping, pre-insulated pipe and fire sprinkler systems in residential and commercial structures around the globe.

Today, three scientific methods exist for producing PEX.

  • Engel method (PEX-a)
  • Silane method (PEX-b)
  • E-beam (electron beam) or radiation method (PEX-c)

What’s the difference between PEX-a, PEX-b and PEX-c tubing?

Engel method (PEX-a)

  • The crosslinking is done during the manufacturing process when polyethylene has no particular shape. This lack of form or shape is called the amorphic state.
  • The degree of crosslinking reaches around 85%, resulting in a more uniform product with no weak links in the molecular chain. This is the highest degree of crosslinking for all the PEX tubing types.
  • Uponor PEX uses the Engel-method (PEX-a) manufacturing process.

Silane method (PEX-b)

  • The crosslinking is done after the extrusion process by placing the tubing in a hot water bath or steam sauna.
  • The degree of crosslinking for PEX-b is typically around 65 to 70%.
  • Because PEX-b is not as evenly crosslinked as the PEX-a method, it doesn’t have the same degree of thermal memory, so kinks in the tubing can’t be reshaped with a simple shot of heat from a heat gun.

E-beam method (PEX-c)

  • The crosslinking is done after the extrusion process by using an electron beam to change the molecular structure of the tubing.
  • The PEX-c method requires multiple passes under the beam to reach a 70 to 75% degree of crosslinking.
  • Side effects of this process are discoloration due to oxidation (from natural white to yellow, unless other pigment is added), and a slightly stiffer product.

Because PEX-a is the most flexible of all the PEX types, and it is also kink-reparable, it gives installers a higher performing product and provides homeowners the peace of mind they need in a plumbing or HVAC system. Because of this reliability, PEX-a is widely considered the superior PEX tubing on the market.