Which of the following is NOT a type of plastic commonly used in plumbing?

PTFE, or polytetrafluoroethylene, is indeed not commonly classified under the traditional types of plastic utilized in standard plumbing applications. While it is a plastic, it is primarily known for its non-stick properties and is used in applications such as cookware coatings and electrical insulation. In plumbing, PTFE is more relevant as a thread sealant, often known by the brand name Teflon, rather than as a pipe material.

The other materials mentioned—PVC (polyvinyl chloride), PE (polyethylene), and PB (polybutylene)—are all widely used in plumbing systems due to their suitability for transporting water and their resistance to corrosion and degradation. PVC is frequently employed for drainage, waste, vent systems, and in some instances, potable water. PE is known for its flexibility and is utilized in various pressure and non-pressure applications, such as water service lines. PB, while less common today due to some historical issues, was once widely used for both hot and cold water distribution systems.