What is polybutylene?
Polybutylene is simply a type of plumbing material that was manufactured between the late 70's and early 90's. It is thought that it was installed in over 6 million homes during that time period. Polybutylene was originally thought to be a versatile and inexpensive product to use. However, manufacturing ceased after many allegations that the pipes were rupturing and causing major damage.
Why does it fail?
To make a long story short, Polybutylene pipes are susceptible to small fractures which can become larger over time and can fail. It is also thought that if PB was not installed correctly, it can also fail at the joints and unions (where two pipes are connected).
When PB fails it can either burst and cause immediate damage or it can leak slowly. If it is leaking slowly, undetected because it is behind drywall, it can cause water damage over time and can cause mold to grow. If the PB bursts it can cause major, immediate water damage.