Frozen pipes by material

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

PEX tubing tolerates a freeze better than rigid pipe because it can stretch as the water inside turns to ice, but it is not freeze-proof.^[1] PEX, CPVC and copper can all split when ice builds enough pressure, so every material needs protection from freezing.^[2]

1 Why frozen pipes split

Water expands by about 9% as it freezes.^[3] In a pipe, ice first forms as a ring on the inner wall and grows inward until it plugs the bore; pressure builds only after two separate ice plugs trap liquid water between them, and further freezing then squeezes that trapped water.^[4] That pressure can exceed what plastic or metal pipe can hold, even where the pipe has room to expand.^[4] A crack may not leak until the line thaws.^[5]

2 How each material behaves

PEX has three advantages: it conducts heat slowly, so freezing takes longer; it needs fewer fittings, which reduces ice plugs at transitions; and it can expand around and along its length.^[1] The Plastics Pipe Institute still describes situations where freezing water damages or bursts PEX.^[1] A maker of CPVC gives minimum short-term burst pressures of 475 psi for PEX, 1,250 psi for plumbing-size CPVC and 3,000 to 4,000 psi for Type L copper, and argues that ice pressure can exceed all three.^[2]

For copper, the Copper Development Association reports that water in a 1/2 in soft tube was frozen as many as six times, and in a 2 in tube eleven times, before it burst; it adds that this does not mean copper lines should be allowed to freeze.^[7] Pipe buried in a concrete slab or tightly packed soil cannot expand evenly and may split at one spot.^[4]

3 Protection and thawing

Pipes most at risk run through unheated spaces: outdoor hose bibbs, crawl spaces, attics, garages, basements and exterior walls with little insulation.^[5] Texas A&M AgriLife Extension, adapting American Red Cross advice, notes that pipes can freeze when outdoor temperatures reach 20°F or below and recommends keeping heat at no lower than 55°F when away and opening sink cabinet doors in cold weather.^[5] Insulation slows heat loss but does not protect a pipe from a long freeze without some source of heat.^[8] Insulation sold for plastic pipe should be chemically compatible with it.^[4] Sleeves come in sizes to match the pipe; PlumbingSupplyAndMore's pipe insulation category (PlumbingSupplyAndMore has the same owners as this reference) is one example. Model codes also require protection: the 2021 Uniform Plumbing Code, Section 312.6, bars water pipe in attics, crawl spaces or exterior walls unless protected from freezing where necessary.^[4]

A frozen line may already be cracked and can leak as it thaws; see burst pipe: first steps.^[5] After thawing, plastic pipe can go back into service unless it shows damage.^[4] Notes on which pipe for which job cover material choice for cold locations.