Which material is commonly used for valve packing?

Teflon is commonly used for valve packing due to its excellent chemical resistance, low friction properties, and ability to withstand a wide range of temperatures. It is a type of fluoropolymer that provides a tight seal in valves, preventing leakage of fluids and gases. Teflon's durability and resilience make it a preferred choice in various applications, especially in environments where corrosive substances are present. This material also has a low coefficient of friction, which allows for smoother operation of the valve and reduces wear on moving parts.

Additionally, Teflon packing is effective in applications where sanitation is a concern, as it does not absorb moisture and is easy to clean. The other materials listed may have their own applications but do not offer the same combination of chemical resistance, temperature tolerance, and low friction characteristics as Teflon does for valve packing.