In frame of fractal description, the estimations of molecular characteristics and kinetic flexibility of macromolecular chains of matrix polymer together with the direct experimental evaluations of interphase parameters for disperse-filled rubber composites (in particular butadiene-styrene rubber filled with nanosize shungite particles) the necessity of validation the physico-mechanical properties of interphase layers for correct calculations and prognosis of reinforcement effect of polymer composites filled with nanosize disperse particles is discussed.