Pneumatic valve gasket material and type of choice

gasket can be divided into soft and hard, soft, generally for non-metallic materials, such as cardboard, rubber, asbestos rubber sheet, teflon, etc.
hard for general metal materials or metal asbestos, metal winding with asbestos, etc.
the shape of the gasket has a lot of, have a flat, circular, elliptical, tooth, lens type, and other special shapes.