Abstract: A cost-effective broadband tunable Fabry-Perot interferometer uses entropic, rather than enthalpic, materials to provide the compliant support for the interferometer's movable mirror. Entropic materials exhibit an entropic plateau region over a wide frequency range with a Young's modulus much lower than enthalpic materials, linear elastic behavior over a wide deformation range, and, in certain geometries, energy and stress behavior that tend to stabilize the movable mirror during deformation. The compliant support can be configured in a variety of geometries including compression, tension, sheer and diaphragm and of a variety of materials including elastomers, aerogels or other long chained polymers.