Fillers in elastomers exhibit a tendency for flocculation respectively networking which has a significant effect on the properties of a filled rubber compound. Networking of fillers depends on their attractive potential and the distance between their aggregates. Since, with regard to surface energy [4], the attractive potential is almost the same for all furnace blacks in hydrocarbon elastomers, the distance between aggregates becomes the controlling factor for filler networking. In this study it was pointed out that filler networking has an influence not only on conductivity but also on the dynamic stiffness of a filled rubber compound. To find the right balance of electrical and viscoelastic properties, which is required today for rubber sealings which separate metals of different electrochemical potentials to avoid electrochemical corrosion, first of all an analysis for the percolation threshold for various blacks in a practical EPDM formulation was done. The second investigation contained an experimental design for special soft blacks in a very basic formulation.