PEX-B pipe

Entry in PEX and plastic supply pipe · Updated October 29, 2026 · Written by the Know Your Pipes editors from the sources listed under References

PEX-B pipe is PEX tubing whose polyethylene is cross-linked by the silane method, in which a reactive silane molecule is grafted onto the polyethylene and the cross-links then form as the tubing cures in moisture.^[1][2] Viega describes it as the silane or moisture-cure method, with cross-linking that develops during and after extrusion.^[3]

PEX-B is used for the same jobs as other PEX pipe: hot and cold water distribution, water service and heating.^[1] The Plastics Pipe Institute states that the A, B and C letters are not a performance ranking and that all three types must meet the same product standards.^[1] Viega puts it more bluntly: PEX-B is not a lower grade than PEX-A.^[3]

1 Manufacture

After extrusion, the silane-grafted tubing is cured in a steam "sauna" or a hot-water bath, where moisture completes the cross-linking reaction.^[2] This separates it from PEX-A, which is cross-linked during extrusion by peroxides, and from PEX-C, which is treated with an electron beam after extrusion.^[1] ASTM F876 allows a degree of cross-linking from 65% to 89% for silane-method tubing.^[2] Uponor, a PEX-A maker, gives 65% to 70% as typical for PEX-B and says it is less flexible than PEX-A.^[4]

2 Fittings

The type letter does not decide which joints can be used; Viega notes that the connection method depends on the system, not the manufacturing letter.^[3] What matters is the print line, where the tubing manufacturer lists the fitting standards it has qualified as a system with that tubing.^[1] Fitting systems commonly listed for PEX-B include the following.

Sources for the table:^[1][2]. See crimp rings and clamp rings for how those joints are checked. Cold-expansion fittings to ASTM F1960 are designed around PEX-A's shape memory; they suit a PEX-B tubing only if its print line lists F1960.^[1]

3 Kinks and damage

Makers disagree on heat repair. Uponor says kinks in PEX-B cannot be repaired with heat.^[4] Viega says heat repair works on some products but is slow and the tube is likely to kink again in the same place; it calls cutting out the damaged section and joining it with a fitting the more reliable repair.^[3]

4 Ratings and UV

PEX-B made to SDR 9 dimensions carries the same standard hydrostatic ratings as other PEX tubing: up to 160 psi with 73°F water and up to 100 psi with 180°F water, and some products add a rating of 80 psi with 200°F water.^[1] UV tolerance varies by product and is shown by the second digit of the material code on the print line.^[1] Viega rates its PEX-B tubing for six months of UV exposure.^[3] All PEX should be kept out of sunlight; see sunlight and UV limits.