Yellow PTFE tape (aka Teflon) is used to seal gas pipe threads, and white PTFE tape is used to seal water pipe threads. But is there really a difference between them? I always thought the yellow was specifically formulated to resist methane and other natural gas additives, but an HVAC technician told me that the different colors are just markers so that anyone looking at the pipe can immediately tell if it's gas or water. Other than the color, they're the same. Is he right?
White = Single Density Tape, only for small fittings up to 3/8 inches. Most people don't know this. "Dual Density" tape used to come in white, too, but since white was available for larger pipes, inspectors had no way of knowing if the white tape used on 1/2-inch and larger pipes was really dual density, so they stopped making it.
Yellow = Double Density, for natural gas (methane) pipes from 1/2-inch to 2-inch diameter. In many jurisdictions, you must use double density tape on natural gas pipes, so inspectors check for yellow.
Pink = Triple Density, for NPT threads from 1/2-inch to 2-inch. Again, most people are not aware of this change and hardware stores rarely sell it in the DIY market, but if you are going to do an inspection, this is what you must use now. This also applies to gas and propane lines.
There is also a green (oil-free tape) for medical gas and a gray/silver (anti-seize compound embedded in the tape) for stainless steel and aluminum pipe.Anything over 2 inches must use a sealant.
