Abstract: A self-actuating temperature sensitive seal comprised of a bimetallic C-ring. Differences in the relative rates of thermal expansivity of the inner face and the outer face of the C-ring cause the C-ring to expand or contract in response to temperature variations. Expansion of the C-ring will create a seal, and contraction of the C-ring will remove the seal between the surfaces surrounding the C-ring. The bimetallic ring may also be used in combination with a spring-biased soft seal made of a fluorocarbon polymer, such as Teflon, to form a fire-safe composite seal. In cryogenic applications, the bimetallic C-ring can provide a seal by itself, or as a biasing element within a surrounding soft jacket.