A mold portion of a molding tool for making plastic articles includes a base body defining a cavity surface and having formed therein at least one heating channel, and at least one cooling channel separated from the heating channel and having a cross section which is smaller than a cross section of the heating channel. The cooling channel is positioned hereby closer to the cavity surface than the heat channel and thus is in an area between the heat channel and the cavity surface, thereby defining a cavity-proximal cooling channel and a cavity-distal heat channel. Before the injection process, the cavity surface is heated by the heat channel to a higher temperature than the demolding temperature of the plastic article to be formed. At the end of the injection process, the cavity surface is cooled by the cooling system.