Polybutylene
A gray plastic water pipe used in millions of 1978–1997 homes that fails from the inside — and is no longer code-approved.
Polybutylene (often called Poly-B) is a flexible gray — sometimes blue or black — plastic water-supply pipe installed in several million U.S. and Canadian homes built roughly between 1978 and 1997. The problem is chemistry: chlorine and chloramine in municipal water slowly attack the pipe and its acetal fittings from the inside, so it can grow brittle and rupture with no outward warning. The failures were widespread enough to trigger the Cox v. Shell Oil class-action settlement (around $1 billion), and polybutylene was eventually removed from U.S. and Canadian plumbing codes. Patching doesn't help because the whole system is degrading at once — the only durable fix is to [repipe](/glossary/repipe) the house in modern [supply line](/glossary/supply-line) materials like PEX or copper. If you find Poly-B, see what a full replacement runs in our [cost to repipe a house](/guides/cost-to-repipe-a-house) guide.