PTFE thread tape: grades, standards and how to wrap it

What thread tape is

Thread tape, also sold as Teflon tape, PTFE tape or plumber’s tape, is a narrow film of polytetrafluoroethylene with no adhesive on it. It is wound round the male thread of a pipe, valve or fitting before the joint is screwed together, and fills the small gaps left between the two threads. Teflon is a Chemours trademark for PTFE, as CS Hyde notes; in hardware shops the name is used for any white thread tape.

The Arctic Hayes data sheet for its M700 tape describes a typical spool: unsintered white PTFE, 0.075 mm thick, 12, 19 or 25 mm wide and 12 m long, with service temperatures of up to 260°C depending on type. The same sheet lists water, gas and oxygen approvals, which is why one spool can look like another and still be meant for different jobs.

Grades: density, thickness and pressure

What separates one PTFE thread seal tape from another is mostly density, and density sets how much heat and pressure the joint will take. The Unipak data sheet sets out its range like this:

Grades: density, thickness and pressure

Unipak tape	Length × width × thickness	Density	Temperature	Max pressure	Use named by Unipak
PTFE-TAPE	10 m × 12 mm × 0.075 mm	0.20 g/cm³	−200 to +80°C	10 bar	air and water, threads up to ¾”
UNITAPE	12 m × 12 mm × 0.075 mm	0.35 g/cm³	up to +100°C	20 bar	air, heating and water, up to ¾”
JUMBOTAPE	15 m × 19 mm × 0.20 mm	0.60 g/cm³	up to +160°C	30 bar	¾” to 2”; coarse, damaged or sharp threads
MAXITAPE	12 m × 12 mm × 0.10 mm	0.70 g/cm³	up to +180°C	30 bar	steam and chemicals, up to 1¼”
MULTITAPE	12 m × 12 mm × 0.10 mm	1.00 g/cm³	up to +260°C	60 bar	approved for gas and drinking water
TOPSEAL	12 m × 12 mm × 0.10 mm	1.30 g/cm³	up to +260°C	100 bar	gas, drinking water and oxygen; EN 751-3

For lines that run above 90°C, Unipak recommends a tape denser than 1 g/cm³. By pipe size, it suggests UNITAPE up to 25 mm, MAXITAPE from 25 to 40 mm and JUMBOTAPE from 40 to 65 mm. These are one maker’s names; other brands grade their tape differently, so compare the density and thickness printed on the pack.

Standards printed on the pack

Two standards turn up on PTFE seal tape. BS 7786:2006 covers unsintered tape for general use: 25 to 300 g/m², 0.05 to 0.25 mm thick, in three grades, for −270°C to +260°C. BS EN 751-3, current as the 2022 edition with a 2023 amendment, covers tape for metal threaded joints carrying gas and hot water, in two classes: F for fine threads and G for coarse ones.

Mass per square metre follows from thickness and density. A 0.075 mm tape at 0.35 g/cm³ weighs about 26 g/m², just above the BS 7786 floor; at 0.20 g/cm³ the same thickness gives 15 g/m², below it (our calculation: thickness × density). The Arctic Hayes M700 lists BS 7786, EN 751-3 and DIN-DVGW 30660 among its approvals.

How to wrap a threaded joint

The steps follow the Unipak directions, with the number of turns from RS Components’ guide to PTFE tape:

1. Clean dirt and metal shavings off the male thread.
2. Start at the end of the pipe and wrap in the direction the thread runs, so that screwing the joint up does not unwind the tape. RS describes this as clockwise when you face the threaded end.
3. Keep an even, firm pull so the tape lies tight in the thread, and overlap each turn by half to three-quarters of the tape width.
4. RS gives two to three turns as enough for most standard joints and notes that the right number depends on the tape’s thickness.
5. Use the tape alone, with no grease or paste, and do not back the joint off once it is made up. Unipak allows readjustment only with its denser MULTITAPE and TOPSEAL.

RS lists radiator valves and taps among the threads this thread seal tape is wrapped on, and the same steps apply to the threaded ends of gate valves and the tails of taps.

Gas lines and compression fittings

Not every PTFE tape is meant for gas. In Unipak’s range, only MULTITAPE, TOPSEAL and the thick SEALRITE are approved for gas; the lighter tapes are for water, air, heating and steam. Tape for gas lines is often sold in yellow: Tape Jungle and RS both describe yellow as the gas grade and green as the tape for oxygen lines. Colour is a convention, so look for a gas approval such as EN 751-3 on the pack as well.

Compression fittings are a different case. RS points out that they seal by squeezing a ferrule between the pipe and the nut, not through the thread, so tape there is generally unnecessary.

What to check when you buy

A roll of PTFE thread tape carries most of what you need on its pack:

• Density and thickness. Both should be on the pack; in the Unipak table they decide the pressure and temperature the joint will take.
• Width. 12 mm suits small threads; Arctic Hayes also makes 19 mm and 25 mm, and Unipak uses 19 mm for threads from ¾” to 2”.
• Standard. BS 7786 for general use; EN 751-3 with class F or G for gas and hot water.
• Approvals. For gas, a gas approval; for drinking water, a drinking-water approval. Unipak’s MULTITAPE and TOPSEAL carry both.
• Spool length. The data sheets above give 10 to 15 m per spool.