A gasket is a mechanical seal (rubber, metal, etc.) that is put between two mating surfaces to fill the space and prevent leakage. The flexible gasket seals all imperfections between the mating surfaces.
Material and design significantly influence the function and price of the gasket. Hard PVC plastic gaskets are suitable for many standard applications. PTFE gaskets are recommended for aggressive media. Gaskets made of copper, aluminum or hydraulic gaskets with NBR inserts are mainly used for high pressure applications.