General topology optimization optimizes material layout within a given design space based on structural aspects. In this paper, structural topology optimization is extended to enable optimization of thermal performances. A novel multi-physics interpolation scheme is proposed and its link with 3D-printed structures is explained. Each design variable now has three optimal states: one state represents the surrounding air, having weak structural and thermal material characteristics; another state represents the solid structure with good structural, but less efficient thermal properties; a third state symbolizes a weight-efficient mesh-structure, improving the structure's thermal conductivity while retaining some structural integrity. The optimi...