One emerging market for electrically conductive resins is for bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases composite electrical conductivity and viscosity. Current technology often adds as much of a single type of carbon filler as possible to achieve the desired conductivity, while still allowing the carbon-filled thermoplastic matrix material to be extruded and molded into a bipolar plate. In this study, varying amounts of two different types of carbon, one carbon black and one synthetic graphite, were added to Vectra A950RX liquid crystal polymer. The resulting single filler composites were then tested for electrical conductivity and rheological properties. The electrical conductivity followed that typically seen in polymer composites with a percolation synthetic graphite. Over the range of shear rates studied, the viscosity followed a shear-thinning power law model with power-law exponent (n - 1) = -0.5 for neat Vectra A950RX and (n - 1) = -0.7 for highly filled composite materials. Viscosity increased with increasing filler volume fraction for all shear rates. The viscosity-enhancement effect was more rapid for the composites containing carbon black when compared with those containing synthetic graphite. (c) 2006 Wiley Periodicals, Inc.