To achieve a successful seal, the gasket must be resilient enough to conform to any irregularities on the mating surfaces. The gasket must also be sufficiently tough or rugged enough to resist extrusion. It must resist creeping and blowing out under operating conditions, as well as unexpected pressure/temperature excursions.
The seal is created by the clamping forces acting upon the gasket surface, compressing the gasket and causing the gasket to conform to flange imperfections. As the gasket material conforms to the flange surface under the compressive load, any potential leak-paths are filled. This prevents the escape of the contained fluid from the bolted flange connection while maintaining a gas-tight seal.