Self-sealing PILAFLON seal ring with built-in spring, featuring the excellent sliding performance of PTFE and followability of the built-in spring. It can be used in gland width and depth size equivalent to those for elastomer O-rings. Thanks to a compact sealing face, it exhibits high performance in a wide range of applications. For example, in static apparatus, it can be used as a gasket, and, in reciprocating machine and low-speed rotating equipment, it can be used as a shaft seal.