A new method has been developed for measuring the thermal conductivity of polymeric materials. The method is based on heat capacity measurements made using modulated differential scanning calorimetry (MDSC). This technique is capable of quantitatively separating reversible (heat capacity related) thermal events from nonreversible thermal events. The advantages of the method are that it is fast and leads to accurate thermal conductivity measurements.The new method was used to measure thermal conductivity of 43 polymeric parts. The results show that crystalline polymers have higher thermal conductivity than amorphous polymers. For any one polymer, thermal conductivity increases with an increase in filler concentration. In the case of polymeric foams, the density of the foam has the major effect on the value of thermal conductivity, although other variables, such as the foam cell size and geometry, and the type and amount of polymer and filler used for making the foam, need to be considered. In the temperature range between glass transition and melting, thermal conductivity decreases as temperature goes up. Measured thermal conductivity values will be used for calculating materials constants for ignition and combustion.