Sunlight and UV limits for plastic pipe

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

PVC UV exposure, meaning sunlight on PVC, CPVC or ABS pipe, discolors a very thin surface layer and lowers the pipe's impact strength, while PEX tubing has strict, maker-set limits on how long it may see sunlight at all.^[1][2] No plastic pipe is immune to sunlight; the differences lie in how much it tolerates and how it is protected.

1 PVC, CPVC and ABS

Ultraviolet (UV) light changes the plastic only at the exposed surface, to a depth of roughly 0.001 to 0.003 in, and the effect stops when exposure stops.^[1] White PVC turns yellow to brown, and colored pipe bleaches.^[2] Research cited by one PVC maker found that impact strength was the only performance property reduced; pressure capacity and pipe stiffness were not affected.^[2] Sun-exposed pipe therefore needs more care against knocks and drops.

Standard PVC pipe compounds contain enough titanium dioxide UV screen to be stored outdoors for at least one year, but pipe meant for outdoor service should be made from a weather-resistant formulation.^[3] Black ABS contains carbon black, which lets it serve outdoors, as on exposed vent pipes, whereas ABS made without it is not advised for outdoor service.^[3] CPVC exposed to sunlight after installation should be painted with a compatible latex paint, according to its compound maker.^[4]

The common protection for above-ground PVC, CPVC and ABS is a water-based latex paint applied to clean, dry pipe; petroleum-based paints should not be used.^[1] An opaque wrap also blocks UV, and burial gives complete protection.^[1]

2 PEX

PEX tubing is more sensitive. The second digit of its material code records tested UV resistance: 1 means one month, 2 means three months and 3 means six months.^[5] Exposure limits differ by maker and color; one maker rates its white PEX for one month of UV exposure and its red and blue PEX for six months.^[6] Makers base their limits on testing to ASTM F2657, using central Arizona sunlight as the worst-case North American location.^[7]

Industry guidance says PEX should not be stored or installed where direct or reflected sunlight reaches it, and should not run outdoors unless buried or protected.^[7] Where PEX will see continuous daylight after installation, such as in an unfinished basement, installers cover it with a UV-blocking sleeve or insulation the maker approves.^[7]

Related reading: frozen pipes by material and which pipe for which job.