This investigation highlighted the equivalence between carbon black (CB) loading and structure influences on dynamic mechanical properties in the linear behavior of several filled synthetic rubber compounds. Different morphologies (specific surface area and structure) of CB incorporated at different loadings were formulated to modulate the filler-rubber matrix interphase content, usually named "tightly bound rubber." Both reinforcement level and tightly bound rubber content were measured on each compound by dynamic mechanical analysis (DMTA) and by Soxhlet extraction and thermogravimetry (TGA) respectively. Then, a systematic description of their evolution was made against CB loading and morphology. These evolutions were attributed to the hydrodynamic effect which could be evaluated by the effective filler volume fraction. A new parameter kappa is defined, representing the effective filler volume fraction for each compound and it was calculated on the basis of experimental parameters. Results show good correspondences between kappa included both the hydrodynamic effects of the filled carbon black rubbers and dynamic mechanical properties. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2715-2723, 2010