In some examples, preheat three-dimensional (3D) printer build material can include a heating plate of a 3D printer to preheat build material from below the build material, where the heating plate is located adjacent to a build platform of the 3D printer, and a heater-spreader carriage of the 3D printer to preheat the build material from above the build material and spread the preheated build material from the heating plate to the build platform.