The contribution of the filler network to the reinforcement of rubber is discussed for silica and organoclay-filled SBR. Mechanical and dynamic-mechanical experiments are performed to investigate the influence of the filler network and the data are fitted with a theoretical model. The percolation threshold is much lower for the organoclay-filled system due to the anisotropic structure of the filler. Reinforcing and ultimate properties as well as the loss factor (tandelta) are greatly enhanced compared to composites filled with the same amount of isotropic silica. A given value of reinforcement can be achieved at a much lower degree of filling and lower tandelta of the organoclay system though at reduced ultimate properties.