Teflon tape is used for sealing pipe threads. The tape is wrapped around the exposed threads of a pipe before it is screwed into place. Since the material is malleable, deformable and impermeable, it works well under pressure when being forced into small gaps between threads, creating an airtight and watertight seal when the pipe is threaded into a joint. This 43.3' (520") roll of tape measures ½" wide.
Tip: Teflon tape is a polytetrafluoroethylene (PTFE) film, and also goes by the names PTFE Tape, Tape Dope, or Plumber's Tape.