PTFE Tape, known by the trademark Teflon tape. PTFE Tape can be used to lubricate the screw thread, with that allows deeper thread fixing and helps prevent the thread from getting stuck when unscrewed. PTFE Tape can also be used as thread lubricant to help seal joints without hardening.
The PTFE tape used in pipe applications is usually white, but it can also be used in various colors: yellow for natural gas, green for oxygen, etc in the United States, Canada, Australia, and New Zealand; yellow for gas reel, green for reel of drinking water in the UK.
White: for NPT threads up to 3/8 inch.
Yellow: 1/2 inch to 2 inch for NPT threads, usually labeled "gas tape".
Pink: 1/2 inch to 2 inch for NPT threads, safe for propane and other hydrocarbon fuels.
Green: Oil-free PTFE for oxygen lines and certain specific medical gases.
Gray: contains nickel, anti-occlusion, anti-wear and anti-corrosion, for stainless steel tube.
Copper: contains copper particles and is certified as a thread lubricant but not a sealant.