Abstract: In order, in the case of bodies with reversibly-variable absorbence, to adjust the zone of transition from transparent to opaque or vice versa at desired goal temperatures and to give the bodies a preferred form, such as sheet form, they consist of a substantially optically transparent polymeric and/or resinous matrix material (A) and an organic substance (B) which is embedded therein as a dispersed second phase and which is at least partially insoluble therein, and which melts or congeals at the goal temperature of light-absorbence variation, and the refractive index of which, either above or below the goal temperature of the light-absorbence variation, substantially agrees with the refractive index of the matrix material.Such bodies are usable in sheet (or film) form, for example, for temperature-measuring devices, temperature-indicating devices, and slippery-ice warning devices, as well as for devices on glass windows for protection against solar irradiation.