Yellow PTFE tape (aka Teflon) is supposed to be used for sealing gas pipe thread, and white PTFE tape, for water. But is there really any difference between them? I had always thought that yellow was specially formulated to resist methane and other natural gas additives, but an HVAC tech told me the different colors are just markers, so that anyone looking at a pipe can immediately tell if it's gas or water. Other than their colors, they're just the same. Was he correct?
I know from handling it that it is clearly heavier. One or two wraps would be equivalent to to six or eight of the white stuff. It is rated for slightly lower temperature. *** After some minor research, evidently there are differences, however, as I see it, these differences are way beyond the scope of the common everyday amateur or even most professionals, i.e. the yellow stuff is rated for 10,000 Lbs. It is considered double density. The white is considered single density. There evidently is a red type also, that is triple density. The red tape is for large diameter pipe, 2" and above. (I've never seen that). The white is rated for something less than 10,000-Lbs. The yellow is rated for -500*F. The white is rated for -450*F. Are you getting my drift.
If I could add a side note; after running several miles of gas pipe in my time, I never used TFE tape on my joints exclusively. I would always use a pipe joint compound/paste type product, Rectorseal was my go-to choice. One day I was in the process of installing one of my gas pipe jobs. It just happened that the local gas supplier tech showed and was checking on something. They supply gas to thousands of homes in our area. He noticed that I was using Rectorseal. He made a point to come over and thank me for using this product. He said that if all the contractors in the area used this product, his job would be a lot easier. So after all this talk about TFE tape, I wouldn't recommend it. It doesn't seal as well as a good quality joint compound.
The colors mean something, but the meaning has changed over the years so some info may be old. The CURRENT standard is:
White = single density tape and is ONLY good for small fittings up to 3/8 in. pipe. Most people are unaware of this. "Double Density" tape used to come in white as well, but because that could be used for larger pipes, it was impossible for inspectors to know if the white tape used on 1/2" and larger pipe was in fact double density, so they stopped making it.
Yellow = double density, required for natural gas (methane) piping 1/2" to 2" dia. pipe. In many jurisdictions you MUST use double density tape on gas piping, so inspectors will look for yellow.
Pink = triple density, required for NPT threads 1/2" to 2". Again, most people are unaware of this change and hardware stores rarely sell it for the DIY market, but if you are going to get an inspection, this is what you must use now. This is also good for gasoline and propane lines.
There is also green for medical gasses (oil free tape) and gray / silver for use with stainless steel and aluminum pipe (has anti-seizing compounds embedded in the tape).
Over 2" you must use sealing compounds.