Glasses with deposited IR-reflective thin films on one of their surfaces operate as heat mirrors. The films improve optical properties of glazings and, compared with ordinary clear glasses, reduce heat radiation losses. The design of thin reflective coatings is based on the theory of optics of thin films. Optical properties of the films are defined by spectral characteristics such as reflectance, transmittance and absorptance for a given wavelength. The paper deals also with classification of the materials suitable for IR-reflective thin films. Spectral reflectance measurements of glass samples were carried out to determine their optical properties in the spectral range of solar radiation (300 - 2500 nm) and in the long-wave IR region (5 - 11 μm). Spectral optical properties of IR-reflective coatings were calculated for different compositions of the films to obtain coatings with very high light transmittance and IR reflectance.