[en] A metal foil bolometer is discussed. The bolometer incorporates preheating of the molybdenum foil up to a temperature of 1200 K where the wavelength of the emitted radiation is such that quartz fiber optics and a Ge detector working at room temperature could be used. This eliminates the need for IR optics and nitrogen cooled detectors. A theory for correlating the observed temperature evolution of the foil with the energy flux onto the foil is given and a calibration procedure is developed. The bolometer was tested on the rotating plasma device FI which operates with plasmas in the cold gas mantle parameter range. The lowest heat flux that could be detected, with a time resolution of 1 ms, was 3x10⁴ W/m². The systematic errors of the measurement due to uncertainties in material constants, such as the tolerance of the foil thickness, are estimated to be 15%. The results of the measurements were in accordance with what was expected. (Auth.)