Rubber gaskets are elastic elements used to mechanically seal the tiny gap between two mating surfaces or joints. Examples of these surfaces include flange faces of pipes and fittings, mating surfaces of automotive cylinder heads and engine blocks, fuel tank rims, and covers, door rims, frames, etc.

Rubber gaskets seal surfaces by flowing into and filling surface irregularities in rigid components. The sealing effect is created by the components applying a compressive force, which plastically deforms the gasket. The sealing ability of rubbers is due to their elastomeric nature. Rubber, whether natural or synthetic, belongs to a class of materials called elastomers.

Elastomers are a class of highly elastic polymers produced by crosslinking long polymer chains into an amorphous structure. The intermolecular forces between polymer chains are relatively weak; this allows them to reconfigure when pressure is applied. Because of this property, elastomeric gaskets can easily conform to the contours of surfaces, creating a tight seal.