Loose-fill thermal insulation settles to some degree under service condition. This means that the insulation layer will settle and the thickness of the thermal insulation will decrease. It also means that the density and the thermal resistance of the insulation material will change during the service life. This article presents the results of experimental investigation of the dependence of thermal resistance upon the settling of loose-fill thermal insulating materials such as mineral wool and cellulose. The results are presented for values measured in accordance with ISO 8302 for loose-fill rock, glass wool and cellulose materials. In this research the influence of humidity of materials on their thermal conductivity has not been studied.