A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. Gaskets can fill irregularities and allow for less-than-perfect mating surfaces on machine parts. Gaskets are commonly produced by cutting from sheet materials, such as gasket paper, rubber, silicone, metal, cork, felt, neoprene, nitrile rubber, fiberglass, polytetrafluoroethylene, or a plastic polymer. Due to health hazards associated with asbestos exposure, non-asbestos gasket materials are used whenever practical. A few gaskets require an application of sealant directly to the gasket surface in order for them to function properly.