Soft seated vs. Metal seated

The difference is "soft seated" or "metal seated". Soft seated valves are used in gas applications were any leakage is absolutely not tolerated. The materials used are Teflon or ceramic. Metal seated valves can have very tight shut-off, it all depends on the coating, pressure in the line, and the lapping of the surfaces.

Originally Ball valves were designed to have soft seats such as a plastic based material, now there are so many options for valve seats. It all depends on the media of what the valve is going to be used for.