The paper deals with the effect of hollow microspheres added to paint or another polymer coating for open surfaces of a building on the heat loss due to thermal radiation. An approximate theoretical model is suggested, which is based on the spectral calculation of the radiative characteristics of a disperse system and determination of the integral flux of thermal radiation. Calculations are performed for a layer of paint with hollow glass microspheres. It is demonstrated that the microsphere shell thickness has the strongest effect on the reduction of heat loss.