When to use PTFE Teflon Yellow or White tapes or Pipe Dope


The purpose of thread sealant tape (a.k.a. “Teflon tape”) or pipe dope is threefold:

  • First, the lubricant qualities allow male threaded pipe to be turned deeper into female threaded fittings to prevent leaks;
  • Second, it acts as a filler to smooth out micro abrasions or surface irregularities on threads;
  • Third, it keeps the male and female threads from rusting together (a.k.a. seizing);
There were lots of comments about the earlier photo that showed sealant tape wrapped in the wrong direction (thank you for pointing out my oversight). I have since replaced the stock photo with my own and wrote a post titled, How To Correctly Apply Teflon Tape to a Thread for your reference :)


allthumbsdiy-plumbing-ptfe-an-thread-flAN thread is a type of fitting used to connect flexible hoses and rigid metal tubing that carry fluid (it stems from a joint standard by the U.S. Army and U.S. Navy, hence “AN”).

AN thread provides a positive seal that should seal correctly with specified torque torque range with no leaks. The AN should not require a thread sealant.

allthumbsdiy-plumbing-ptfe-npt-thread-flNational Pipe Thread (NPT) taper is a U.S. standard for tapered threads used on threaded pipes and fittings.

In contrast to straight threads that are found on a bolt, a tapered thread will pull pipes and fittings tight together, providing effective seal for pipes transporting liquids, gases, steam and other fluids.

Although SAE and ASTM (organizations that set U.S. industry standards) set very precise thread class specifications, many threaded products carried by large box retailers have varying degrees of deviations from set specifications (i.e. micro surface imperfections like chatter or spalling), thus requiring a use of thread sealants.


In a residential home environment, we are primarily transporting non-caustic substances like water, natural gas, Liquified Petroleum Gas (LPG), fuel oil (and maybe compressed air and oxygen).

Although there is no hard and fast rule, we can broadly categorize residential threaded joints as either permanent or semi-permanent joints to identify appropriate applications for thread sealants:

Joint Type Description Product Suggestion
Permanent Joints Any joints which would normally be installed during the rough-in or stack-out phase of the plumbing and which could be reasonably expected to last the lifetime of the structure. These would include galvanized iron water lines, threaded connections on main & zone valves on the water distribution system and gas lines. Pipe Dope
Semi-permanent Joints Any joints which we typically make during the final trim out phase such as fixture angle stops, shower arms, shower heads, tub spout to the stub outs or any joint which we could reasonably expect may be changed periodically for general maintenance or aesthetics purposes during the life of the structure. Sealant Tape


When a thread seal tape was first introduced, it only came in a single density type (“white Teflon tape(1)“) that was commonly found in large home improvement stores. Later they began making a double density version, which was twice as thick in the same color (unfortunately with the same “white” color).

(1)Teflon tape is used ubiquitously when referring to a thread sealant tape. However, the word “Teflon” is a trademark name owned by Dupont Chemical Corp. Although Dupont no longer manufacturers Teflon tapes, it still enforces its trademark rights. That is why you see other manufacturers like Oatey refers to it as PTFE (PolyTetraFluoroEthylene) thread sealant tapes.

One very important thing to remember is that PTFE thread sealant tapes and pipe joint compounds are only to be used on NPT male threads. Neither should be used on SAE mechanical threads or as a gasket sealer (i.e. sink basket gasket).


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Since many state and local codes adopted the use of double density tapes when making connections for natural gas, the use of same color for two different thickness presented a challenge when time came to inspect a job. Thus, a “yellow TEFLON tape” was later introduced for such application.

Since then, ASTM has broadened the specifications for PTFE tape colors:

Tape Color Description Product Link
White single or double density, should only be used on NPT threads up to 3/8 inch in diameter LASCO White 1/2-Inch Double Density PTFE Thread Seal Tape
Yellow double density, often labeled as “gas tape” Oatey Yellow 1/2-Inch Gas PTFE Thread Seal Tape
Pink triple density, required on all joints 1/2″ or larger LASCO Pink 1/2-Inch High Density PTFE Thread Seal Tape
Green Oil Free PTFE tape, required for use on all lines carrying oxygen (i.e. – medical oxygen or welding oxygen lines) Gasoila, 1/2-Inch Green PTFE High Density Thread Tape, 3.7 mil Thick


Pipe dope, technically known as pipe joint compound is both a thread lubricant and thread sealing compound. Unlike a thread sealant tape, pipe dope is designed to make a pipe thread joint leak proof and pressure tight by brushing on a pasty substance to a male thread (never to a female thread because some of it will push into the pipe.

Some people use pipe dope on top of thread sealant tape but many manufacturers say there is no added benefit to that setup.

Pipe dope itself can be classified into 2 distinct categories:

Pipe-Dope Type Description Product Link
Oil Based Usually comes in a dark gray paste designed to work on all metal based pipes and fittings Oatey Pro Dope
Non-Oil Based Usually comes in a white paste that works with all metal and PVC-based pipes (make sure to read the product label to verify that a given product can be applied to PVC/cPVC threads such as P-traps, tailpieces, waste & overflow, etc.) Rectorseal Pipe Thread Sealant

While there are number of pipe dope product on the market, the one that seems to be most widely accepted by plumbers, pipe fitters, HVAC techs and electricians is a product called “RectorSeal” (Rector Seal #5 is applicable to metal and PVC; Rector Seal #7 is only applicable to metal).

Rector Seal has a comprehensive thread sealant product matrix. click here (non-affiliate) link for review.

If the thread you are working on will be exposed to extreme temperatures, a better suited product might be a liquid thread sealant called Permatex Thread Sealant with PTFE. This product has the same sealing capabilities but it is also designed to work in a broader range of temperatures (-60 to 300 F).


  • The main purpose of a thread seal tape / liquid thread sealant is to seal out micro abrasions or surface irregularities on threads. If you have a major gash or nick on a thread, you will need to replace the pipe section or re-thread it, rather than applying a thicker seal tape layer;
  • Applying more than 3 layers of sealant tape is not recommended;
  • When starting out, make sure the seal tape is not covering the pipe opening. Any exposed seal tape may break loose over a period of time and cause a blockage problem; in the future;
  • Pipe connections generally turn clock-wise but there are instances when that is not true (i.e. gas pipe union joint). Always test out and make a note of the pipe rotation before applying the tape and remember that the tape application must “go with the flow”;
  • You cannot connect dis-similar pipes together (i.e. copper-to-steel) and hope that a thread sealant tape will prevent from interacting with each other, possibly causing corrosion problems. In this situation, you must use a dielectric union (something like this)
  • If you need a gasket sealer, you may want to checkout can use hyolomar based products like Valco Cincinnati Hylomar Compound or Permatex Oil Resistance RTV Silicone Gasket.

Final Thoughts

So what do I use in my plumbing projects?

I tend to apply both the sealant tape and pipe dope if there is plenty of space around the pipe I am working on or if I am working with black steel pipes (generally used for natural gas) because their threads tend to be rougher.

If the working space is tight (let’s say a 1/2″ water pipe straddling a floor joist), I tend to go just with pipe dope.

If you have some time, head on over to the post titled, How To Correctly Apply Teflon Tape to a Thread to see more examples.

Well, I hope you found my post on pipe thread sealants to be useful and signup for my free newsletter. The sign up form is found on the upper right screen and I promise it will be spam free.

Thanks again for reading my post and good luck with your DIY project!



  1. Faz says

    Great Article, thanks for the data.

    For the average DYI’er tho, that top picture is a bit misleading, as:
    1. It’s usually easier to apply the tape under tension with the roll reversed from what is shown, and
    2. That pipe in the picture would have to be left handed thread if the tape was applied as shown – which is not common and only used in some gas fittings – which would also mean that it should probably be yellow tape.

    Obviously a stock photo of some kind, but again, a bit misleading. Cheers!

  2. kevin says


    thanks for the feedback (and yes, it was a stock photo)


  3. Robert Hall says

    The photo above the article is showing the incorrect direction for wrapping Teflon tape (assuming that the pipe has RH threads).

  4. Andy Olejarz says

    I think the photo shows the correct direction, so the exposed tail of the tape doesn’t get mashed up, it goes with the direction of the female threads sliding over it.

  5. kevin says

    Hi Andy-

    Thanks for your feedback. Yes, the earlier comments were made to the stock photo that had incorrect wrapping direction. Since then, that picture has been replaced with my own (what you see now).



  6. JR says

    DuPont name is now Axalta. You may want to update that information before some cooperate freak show tries to shut down your site. Great info, thank you.

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