The objective of this study is to determine the influence of radiant barriers on conductive and radiative heat transfers when they are integrated to a building envelope and to compare their efficiency to traditional insulation material (mineral wools, polystyrene). It is also about determining which insulation material and process can lead to a better heat flux reduction through a building roof. For this study four identical small-scale test cells were used. Their respective roof was equipped with the insulation material to be tested: One with polystyrene, the second with a radiant barrier the third one with fibber glass and the last one with no insulation material was considered as the reference cell. Different test were performed with a view to evaluate the influence of parameters such as roof absorptivity and roof air layer ventilation on the heat flux reduction through the roof. With the measured temperature, the conductive and radiative heat fluxes were calculated. With a white corrugated iron roof top the heat flux reduction provided by the radiant barrier is 37%. With a black one this material allows a reduction of 33%. It is shown that whatever the roof absorptivity value, the radiative heat flux is predominant over the conductive one. With no ventilation, the radiant barrier is comparable to polystyrene and fiber glass; when the airspace is ventilated the radiant barrier provides a better insulation. (c) 2004 Elsevier Ltd. All rights reserved.