Short definition
Polybutylene (PB) is a flexible plastic supply pipe widely installed in US homes from approximately 1978 to 1995. It’s typically gray inside and blue or black outside, often with brand markings “Qest,” “Big Blue,” or “PB-2110.” It fails unpredictably from chlorine attack and acetal-fitting failure, was the subject of a 1995 class-action settlement, and is a standard repipe target. Not approved under current US plumbing codes.
What it is
PB is the flexible plastic that almost made it. From the late 1970s through the early 1990s, it was installed as the cheap-and-easy alternative to copper for both interior supply (gray PB) and underground service lines (blue or black PB). Joined originally with crimp rings on acetal (plastic) fittings — which were the weakest link in the system.
The failure pattern is what made PB famous. Chlorine in tap water attacks the plastic over time, producing micro-cracks and brittle fracture. The acetal fittings were even more vulnerable; later metal-fitting versions had longer life but the pipe itself remained problem-prone. Failures are random — a PB system that’s been working fine for 20 years can produce a flooding rupture without warning.
The 1995 Cox v. Shell Oil class-action settlement compensated US homeowners. New manufacturing largely ceased in the late 1990s, and PB was removed from US residential plumbing codes for new construction. It was never approved under Washington’s UPC adoption (WAC 51-56).
Why it matters to a homeowner
If you’re buying or own a 1978–1995 home and the supply piping is gray plastic, this is what you’re looking at — and the prudent move is replacement, not waiting:
- Insurance impact. Many WA homeowner’s insurance carriers now decline to write or renew coverage on homes with active PB plumbing, or write only with elevated premiums and explicit exclusions for PB-related water damage.
- Real-estate impact. Inspectors flag PB; buyers routinely request a credit equal to the cost of a full repipe.
- Repipe to PEX is the standard remediation. Cost in Washington typically $4,000 to $12,000 depending on home size and access.
Common failure modes
- Brittle fracture from chlorine attack on the pipe walls.
- Acetal fitting failure — original gray plastic fittings.
- Crimp ring corrosion at metal-banded fittings in damp locations.
- Random pinhole leaks in long runs — not predictable by visual inspection.