Open cell metal foams increasingly find lots of applications in modern energy systems. For example, they improve the efficiency of low-energy modules based on paraffin wax. In this work, the effective thermal conductivity of selected composite materials based on open cell foam solids is calculated by means of computer simulations. The results are compared with appropriate experimental values with a very good agreement. The characteristic constants for three material laws (Bhattacharya, Ashby and Maxwell) are found. The range of validity of these laws is narrowed to enable the well-directed use of them in the future.