Increasing the thermal conductivity of typically insulating polymers opens new markets. A thermally conductive resin can be used for heat-sink applications. This research focused on extruding followed by injection molding and thermal conductivity testing of carbon filled nylon 6,6 and polycarbonate-based resins. The three carbon fillers investigated included an electrically conductive carbon black, synthetic graphite particles, and a milled pitch-based carbon fiber. For each polymer, conductive resins were produced and tested that contained varying amounts of these single carbon fillers. In addition, combinations of fillers were investigated by conducting a full 2(3) factorial design and a complete replicate in each polymer. These through-plane thermal conductivity experimental results were then compared to results predicted by several different thermal conductivity models. An improved thermal conductivity model was developed that fit the experimental results well for resins that contained single fillers and combinations of different fillers. This improved model was based on the original Nielsen model. A single value for the shape parameter, A (which is needed in Nielsen's model), was used for all three different fillers. (C) 2003 Wiley Periodicals, lnc.