Accurate data have been obtained on the thermal conductivity of six grades of manufactured graphite. In particular, the effect of orientation, manufacturing process, and impregnant content on the thermal conductivity was investigated. Using the thermal conductivity data, a three-dimensional finite-element model has been set up to determine the wall resistance of a particular graphite block. The effect of the anisotropy of the extruded graphite on the wall resistance was investigated. It was found that the anisotropy can be neglected if the wall resistance is calculated by assuming that the blocks have an isotropic thermal conductivity equal to the thermal conductivity perpendicular to the direction of extrusion. Also, the phenol formaldehyde film on the surface of the heat exchanger channels was determined to have a significant thermal resistance. It was calculated that, for typical operating film coefficients with water on both sides, the overall heat transfer coefficient can be expected to increase by more than 50% if the resin layer is removed.