There's no single type of plastic used to manufacture pipes. For years, a gray plastic called polybutylene was common for plumbing systems, but it's no longer used because it splits and creates leaks. If you have old polybutylene pipes in your house, we strongly recommend you arrange to have it replaced with a newer type of plastic pipe. Here are the three types of plastic water pipes that are commonly used by plumbers today http://www.ifanplast.com/plastic-pipe/