Mechanical properties of different rubber composites like (i) styrene butadiene rubber (SBR) filled with silica nanoparticles and (ii) natural rubber (NR) filled with carbon black (CB) or carbon nanotubes (CNT) are studied. Of special interest are contributions to reinforcement caused by the “filler network” in composites with higher filler contents. Central aim of this work is to quantify and to understand the factors influencing overall reinforcement and to compare the filler network contributions depending on temperature and frequency in CB and CNT filled NR with those obtained for SBR containing silica. Temperature-dependent shear measurements show that the storage modulus G’ in the plateau range decreases significantly with increasing temperature for all composites that contain large filler fractions above the percolation threshold. This decrease of G’ is interpreted as a first indication for the existence of a glassy rubber layers located on filler surfaces which soften gradually at higher temperatures than corresponding bulk rubber. Consistent with this observation, low-field NMR studies on SBR composites confirm the existence of a small fraction (a few percent) of immobilized rubber which becomes smaller with increasing temperature. The filler network strength is quantified based on dynamic strain sweeps performed at different temperatures and frequencies which are analyzed using the Kraus model. The results show that the load carrying capacity of the filler network, defined by the difference of the storage moduli obtained at small to large deformations, depends systematically on temperature and frequency. This shows that visco-elastic elements exist in all filler networks under investigation despite of significant differences regarding the filler network topology. A detailed comparison made in this study contributes to a better understanding of the reinforcement mechanisms in composites which is prerequisite for their efficient optimization for tire treads.