The paper the possibilities of design of the heat-conducting compositions on the polymeric basis are investigated. These possibilities realize by the structural modification of polymers due to the filling with their reinforcing particles, whose thermophysical characteristics considerably are differed from the appropriate properties of matrix. The methods of calculating the coefficient of the thermal conductivity of polyphase materials by different methods are described, including based on the solution of the problem of thermal conductivity by the finite element method. In the paper the comparative analysis of the results of determining the coefficient of the thermal conductivity of the filled materials, obtained by experimental and calculated methods, is carried out. This makes it possible to estimate the authenticity of the obtained values and limit of the applicability of the proposed models and their realizing methods. It is shown, as with the use as the filling of materials with different thermophysical characteristics, in particular, with the different coefficients of thermal conductivity, and also by changing the degree of filling, it is possible to change the appropriate properties of compositions in the necessary direction. The given results are obtained for the materials on the basis of different polymeric matrices with different thermophysical properties. The described method of determining the effective characteristics of the filled compositions shows that the obtained with its aid of the value of effective coefficient thermal conductivities not only it is qualitative, but also quantitatively they will agree with the experimental data.