To go ahead in understanding the nature of rubber reinforcement and evaluate the kinetics of filler clusters destruction during stretching of filled rubber, the styrene-butadiene rubber both unfilled and filled with various contents of silica particles with and without surface treatment was tested under quasistatic loading up to failure. The Klueppel-Schramm model was used for description of strain softening, evaluation of both the rubber and filler network parameters as the functions of the filler volume content. It was found that an elastic modulus as a function of filler volume content follows Guth-Gold equation, confirming the hydrodynamic nature of the rubber reinforcement; the effectiveness factor depends on filler surface treatment. Hydrodynamic amplification factor increases with increase of filler volume content, its value depends on filler particles surface treatment. The decrease of hydrodynamic amplification factor during stretching correlates with the increase of viscoelastic strain. Taking into account the viscoelastic strain improves the description of the stress-strain response of filled rubber for loading-unloading process with the parameters obtained for active loading. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1621-1629, 2012