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Polybutylene Supply Pipe

Fitted widely from the late seventies until 1995, then discontinued. Worth identifying if your home is from that window — but it fails differently.

Hand press clamping a press fitting onto plastic supply pipe, more fittings alongside

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Polybutylene is a gray (sometimes white or silver) flexible plastic supply pipe, usually about half an inch or an inch across, often marked PB2110. It was installed widely in American homes from the late 1970s and stopped being used in 1995.

Why it is different from a pressure problem

This matters for diagnosis. Galvanized steel fails gradually — the bore narrows over decades and pressure declines slowly. Polybutylene does not narrow. Its failure mode is sudden: the material and its fittings become brittle and let go. So polybutylene is rarely the explanation for pressure that has been slowly fading.

If your pressure has dropped gradually in a house of this era, the more likely causes are the pressure-reducing valve or a part-closed valve.

Old metal supply pipes running across a basement ceiling

How to identify it

Gray, flexible, not rigid like copper or steel.
Often stamped PB2110.
Look at the water heater, under sinks, and where pipes enter through walls.
Fittings may be plastic or metal with crimped rings.

What to do about it

Identification is worth doing on its own account — it affects insurance and it affects what you tell a buyer. But it is a repiping question rather than a pressure question, and whether to act depends on what is accessible and how much of the original run is left. That is a decision for someone standing in the property.