Plumber's Tape (PTFE Tape)

Plumber's tape — officially called PTFE tape (polytetrafluoroethylene) and commonly called Teflon tape — is a thin, white, non-adhesive tape wrapped around threaded pipe fittings before assembly. It fills microscopic gaps in threaded connections, creating a leak-free seal on pressurized supply lines.

How do you apply plumber's tape correctly?

1. Start at the first thread of the male fitting
2. Wrap clockwise when looking at the end of the pipe (same direction you'll tighten the fitting)
3. Apply 2–3 wraps, stretching the tape slightly so it seats into the threads
4. Tear the tape and press the end flat
5. Thread the fitting on by hand first, then tighten with a wrench

Wrapping the wrong direction is the most common mistake — if you wrap counterclockwise, the tape bunches and shreds as you tighten, defeating the seal entirely.

What do PTFE tape colors mean?

• White — standard, for water supply lines (NPT threads)
• Yellow — thicker, rated for gas lines (do not substitute white on gas)
• Pink — rated for potable water supply with NSF 61 certification
• Blue/Green — oxygen lines and specialty gases

When should you not use PTFE tape?

Tape belongs on tapered threads that seal by wedging — NPT pipe threads — and nowhere else. Three joints are routinely ruined by it:

• Compression fittings — the seal is the brass ferrule crushing onto the tube. Tape on the nut threads only lets the nut turn further before it feels tight, which over-crushes the ferrule.
• Flare fittings — the seal is metal-to-metal between the flared tube and the fitting cone. Tape does nothing there and can hold the faces apart.
• Slip-joint and tailpiece nuts under a sink — a nylon or rubber washer makes that seal. Tape on those straight threads is the usual reason a trap keeps weeping after it has been taken apart and reassembled.

Plastic female threads deserve their own caution. Tape reduces friction enough that a fitting can be turned well past hand-tight without feeling resistant, and the wedging action of the tapered thread then splits the plastic — sometimes days later, once the joint has been under pressure.

PTFE tape or pipe dope — which should you use?

Tape is cleaner and easier for DIY use. Pipe dope (a paste) provides a stronger seal on older, coarser iron pipe threads and in high-vibration applications. Professional plumbers often use both together on critical connections.

A roll of standard PTFE tape costs $1–$3 and is one of the most used items in a plumber's kit.