PTFE tape is a film cut to specified widths for use in sealing pipe threads. The tape is wrapped around the exposed threads of a pipe before it is screwed into place. Since the PTFE is malleable, deformable and impermeable, it acts a little like putty under compression, being forced into small gaps between threads in order to create an air and watertight seal when threaded into a joint. The tape is commonly used in pressurized water systems, such as irrigation systems.