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PEX-A pipe

Entry in PEX and plastic supply pipe · Updated · Written by the Know Your Pipes editors from the sources listed under References

PEX-A pipe is cross-linked polyethylene tubing made by the peroxide, or Engel, method, in which organic peroxides release free radicals that join the polyethylene chains while the tube is being extruded.[1] It is used for hot and cold water distribution, radiant heating and water service, like other PEX pipe.[1]

The "A" names the manufacturing method, not a grade. The Plastics Pipe Institute states that the letter designations are not related to any performance rating and that PEX-A, PEX-B and PEX-C must meet the same product standards.[1]

1 History

According to Uponor, German inventor Thomas Engel developed a method of chemically cross-linking polyethylene in 1968, and the company Wirsbo (later Uponor) introduced Engel-method PEX to the European market in 1972.[4] PEX reached the United States and Canada in 1984.[2]

2 Manufacture

In the peroxide process the cross-links form during extrusion, rather than in a separate curing step afterward as with the silane method.[1][2] ASTM F876 sets a degree of cross-linking between 70% and 89% for peroxide-method tubing, against 65% to 89% for the silane and electron-beam methods.[2] One maker, Uponor, says its Engel-method tubing is cross-linked to 80% or more.[4]

PEX-A compared with the other two types
TypeCross-linking methodASTM F876 cross-link range
PEX-APeroxide (Engel), during extrusion70% to 89%
PEX-BSilane, moisture cure after extrusion65% to 89%
PEX-CElectron beam, after extrusion65% to 89%

3 Flexibility and shape memory

Makers describe PEX-A as the most flexible of the three types; Uponor says PEX-B and PEX-C are less flexible.[6] Its elastic "shape memory" lets the tube end be stretched with an expansion tool and then shrink back over a fitting.[6] Uponor also says a kink in PEX-A can be repaired with heat from a heat gun (never an open flame) where its instructions allow, and that this is not possible with other PEX types.[4] Other makers' instructions differ, and a damaged section can always be cut out and joined with an approved fitting.

4 Fittings

Cold-expansion fittings are the joint most closely tied to PEX-A. ASTM F1960 fittings use a PEX reinforcing ring slid over the tube end before it is expanded; ASTM F2080 fittings use a metal compression sleeve instead.[1] As the tube recovers its shape, it grips the fitting. See PEX expansion fittings.

Much PEX-A tubing is also listed for crimp rings, stainless clamp rings and push-fit fittings, but only the systems printed on that tubing's print line are approved for it.[1][5]

5 Ratings and identification

Pressure ratings for SDR 9 PEX-A tubing are the same as for other PEX: water at 73°F is rated to 160 psi, at 180°F to 100 psi, and, for listed products, at 200°F to 80 psi.[3] The print line carries a four-digit material code such as "PEX 5306": the first digit is chlorine resistance, the second UV resistance and the last two the design stress.[2][5] A UV digit of 3 means at least six months of tested exposure; 1 means one month.[2] Uponor rates its white tubing for one month of sunlight and its red and blue tubing for six.[4] How to read the rest is covered in reading pipe markings.

See also

  • PEX pipeFlexible cross-linked polyethylene tubing for hot and cold water, rated 100 psi at 180°F and joined with mechanical fittings.
  • PEX-B pipePEX tubing cross-linked by the silane (moisture-cure) method; commonly joined with crimp, clamp, press or push-fit fittings.
  • PEX expansion fittingsFittings joined by stretching PEX tubing and a ring, then letting the tube shrink back onto the fitting; ASTM F1960 and F2080.
  • PEX-C pipePEX tubing cross-linked by an electron beam after the tube has been extruded.
  • CPVC pipeRigid chlorinated PVC water pipe in copper tube sizes, rated 100 psi at 180°F and joined with CPVC solvent cement.
  • PP-R pipePolypropylene random-copolymer pressure pipe, joined by heat fusion, used for plumbing and hydronic systems mostly in larger buildings.

References

  1. Plastics Pipe Institute, "TN-17 Crosslinked Polyethylene (PEX) Pipe & Tubing Systems" (2021) — plasticpipe.org
  2. Plastics Pipe Institute, "Designing PEX Plumbing Systems to Optimize Performance and Efficiency" (2020) — conduitcalc.plasticpipe.org
  3. Uponor, "Uponor AquaPEX white straight lengths" submittal (2026) — uponor.com
  4. Uponor, "Customer support FAQ" — uponor.com
  5. Uponor, "Understanding the Print String on Uponor PEX-a Pipe" (2024) — uponor.com
  6. Uponor, "Not All PEX Is Created Equal: Why Choosing the Right Type Matters" (2025) — uponor.com