Abstract Thermal conductivity, diffusivity, effusivity and specific heat of polypropylene matrix filled with copper particles of two different sizes were investigated. A parallel study of the evolution of the electrical conductivity was also carried out. The highest heat transport ability was observed for the composites filled with the smaller particles. Electrical conductivity investigations showed that the size of fillers also influences the percolation threshold. The Agari's model provides a good estimation of the thermal conductivity of composites for all filler concentrations. It was used in order to give a comparative analysis of both electrical and thermal properties of such two-phase systems. Nevertheless, the physical meaning of the two fitting parameters C1 and C2 of Agari's model has to be completed.