This work is a contribution to understand the thermal properties of Illite with ecological additives granular presented by cork or fiber by wool in order to use those composites in building construction, the composites are air dried. Knowing that the clay composites were studied before, a series of experimental studies confirmed by complete theoretical models were conducted using different methods such as the asymmetrical hot plate in transient, steady-state regime, and flash methods in order to determine the thermal properties of the composite clay with ecological additives. Also, an analysis of sensibility of thermal properties was studied. For this purpose, a thermal characterization using hot plate and flash methods confirmed by complete theoretical models was studied. Then an analysis of the physicochemical characterization of clay was done to determine its characteristics. Finally, a study of depth heat flow diffusion was conducted to see the effect of additives on penetrating exterior heat flow inside house.