Creep is deformation with time when a part is subjected to constant stress. Metals creep can occur at elevated temperature however with gasket materials it can occur at normal ambient temperatures. Creep resistance is an important property of gasket materials. Gasket materials are designed to flow under stress to fill any irregularities in the flange surface. The amount of creep sustained tends to increase with temperature. However once the tightening is completed it is important that no further flow occurs since such deformation will lead to a reduction in bolt extension and subsequently the stress acting on the gasket. If this stress is reduced to below a certain minimum, which depends upon the type and construction of the gasket and the operating temperature, a high rate of leakage can be anticipated to occur.