Because of their preferred orientation, the addition of boron nitride dispersions to hot‐pressed boron carbide was found to result in a considerable degree of anisotropy in thermal conductivity of the resulting composite, indicated by an increase in the thermal conductivity perpendicular to the hot‐pressing direction by as much as a factor of 3 at the highest boron nitride volume fractions of this study, and a decrease in the thermal conductivity parallel to the hot‐pressing direction by as much as a factor of 2. The composite data were found to be below the values expected from composite theory, which may represent indirect evidence for the existence of an interfacial thermal ba