Based on the model approach, we propose a description of elastic properties of high elastic polymer-matrix composites filled with rigid particles in accounting for the properties of interphase layers. We form an estimate of the influence of the molecular and structural characteristics of interphase layers on the mechanical properties of composites. On this basis, we obtain the range of values within which it is necessary to take into account the influence of interphase layers on the mechanical properties of composites. We obtain the analytic formula that relates the elastic modulus of shear of the composite material to the structural parameters of the composite and the macroscopic properties of the interphase layer. We perform an estimate of the lower bound of influence of the parameters of the interphase layer on the elastic properties of rubber-like composite materials. From this we conclude that the allowance for the influence of these parameters leads to a variation of 20% for the shear modulus of composite materials.