The heat transfer in a highly conductive material constituted by a graphite matrix in which a granular phase is dispersed is studied. The effective thermal conductivity of this anisotropic porous composite medium used in solid-gas reactors can vary largely with the component fractions. The effect of the dispersed grains on the deformable structure of the matrix is considered. A model developed on the basis of thermal tortuosity by analogy with mass transfer is adequately correlated with experimental results.