This research study investigates the influence of heat treatment on the thermal conductivities of three different tool steels at room temperature. The results reveal not only that tempering plays a decisive role in their thermophysical properties, but also that the changes in thermal conductivity due to heat treatment are dependent on the degree of alloying. Isobaric heat capacities c (p) are found to be less dependent on heat treatment than thermal diffusivities a. The results are discussed with respect to the resulting microstructures and, for high-tempered conditions, under consideration of Calphad calculations. The results are relevant for the thermal design of tools, in particular, for tailored tempering of tools used for press hardening.