Carbon fibers with a high thermal conductivity are used to enhance the thermal conductivities of energy storage media. Two types of enhancement techniques were studied. One is the technique using randomly oriented fibers, while the other is that of using a fiber brush. The carbon fibers essentially enhance the effective thermal conductivity of fiber/paraffin composites. For the random type, the fiber length has little effect on the effective thermal conductivity. The fiber brush increases the effective thermal conductivities to the maximum values predicted which is theoretically. The fiber brush is also useful for enhancing the effective thermal conductivities of packed beds of particles.