PTFE Thread Seal Tape: Colour Codes, Wrap Direction, and Limits

PTFE thread seal tape — sold as plumber's tape, Teflon tape, or ФУМ-лента — is a thin unsintered polytetrafluoroethylene film wound onto a male thread before assembly. It is the default thread sealant in Anglo-American plumbing, where fibre-and-paste is the continental default: Thread Sealant Selection: Flax and Paste, PTFE Tape, Anaerobic, and Wound Cord. ## How it works The tape is not an adhesive and not really a gasket. Under assembly torque the unsintered film cold-flows into the thread's helical leak path and, because PTFE has an extremely low coefficient of friction, it also lubricates the joint so a tapered thread can be pulled up tighter for the same torque. Both effects contribute to the seal. ## Wrap direction Wind in the direction the mating fitting will turn — clockwise looking at the open end of a right-hand male thread — so tightening drags the tape further into the threads rather than peeling it off. This is the same rule that governs winding flax tow, and the same mistake accounts for most failed joints. Two to three wraps suits most threads; more is not better, and excess tape shears off into the pipe where it can foul a valve seat or a cartridge. ## Colour coding Colours are conventional and widely followed, though not universally mandatory: - **White** — general purpose, water, thinnest, most common - **Yellow** — gas grade, thicker and denser, for fuel gas lines - **Pink** — heavy-duty water, thicker than white, for larger threads - **Green** — oil-free, for oxygen service - **Grey** — filled with stainless particles, anti-galling for stainless threads ## Limits The polymer itself tolerates a wide temperature range, roughly −60 °C to +240 °C, and the tape is generally rated to around 20 bar in service. In practice the limits that bite are mechanical: the film tears and shreds on rough, corroded or damaged threads, and it becomes unreliable much above 50 mm diameter, where the leak path is too large for a thin film to fill. Plumbers working heating systems often set a working ceiling near 120 °C and switch to fibre and paste above it. Tape does **not** make a joint adjustable. Backing a fitting off to aim it breaks the seal and the joint must be stripped and re-wrapped — the practical advantage that keeps flax in use on valves and elbows. For drinking water, PTFE tape is accepted under all three major regimes (WRAS in the UK, NSF/ANSI 61 in the US, DVGW in Germany), which is not true of hemp: Hemp Thread Sealing and Drinking Water: Approved in Germany, Banned in the UK.