A cured vinyl ester resin containing electrically conductive carbon black (CB)particles shows electrical percolation at very low CB concentration (<0.5 phr). CB particles have a strong tendency to agglomerate in a low-viscosity resin, such as vinyl ester, unsaturated polyester resin, and epoxy resins. The agglomeration process in the low-viscosity vinyl ester resin generates electrically conductive paths already in the resin＇s liquid state, which undergo partial fixation by room temperature curing and full fixation by hot postcuring. The fully cured castings containing CB concentrations above percolation are characterized by a constant, temperature-independent conductivity, over a wide temperature range. The current-voltage relationships of the cured vinyl ester/CB castings obey a power-law dependency. The presence of the continuous CB paths in the vinyl ester casting is clearly observed in fracture surfaces formed at 100 degrees C. (C) 2000 John Wiley & Sons, Inc.