Anett Király, Ferenc Ronkay - Department of Polymer Engineering, Budapest University of Technology and Economics - We prepared conductive polypropylene sheets with different compositions of carbon black and hybrid carbon black/graphite fillings and investigated the effect of the filler on the flowability and electrical conductivity. Optical microscopy studies demonstrated that the carbon black content not only directly but also indirectly affects the electrical conductivity and viscosity of the hybrid materials by having a significant effect on the graphite dispersion, so that the processability and conductivity are inversely affected with increasing filler content.