Designs generated by topology optimization are often geometrically too complex for conventional manufacturing techniques. While additive manufacturing holds promise for producing such complex designs, several manufacturability constraints must be addressed, including overhang and overheating. Unlike the well-studied overhang constraints, which can be described geometrically, overheating lacks a straightforward and reliable geometric characterization and therefore requires thermal process simulations to identify regions prone to it. However, these simulations are computationally expensive and thus unsuitable for topology optimization, which involves numerous design evaluations. This paper proposes a computationally efficient alternative for detecting zones prone to overheating. The key idea is to estimate local thermal conductivity—and thereby potential overheating—by analyzing the local material distribution. This geometric approach provides a physically motivated approximation of thermal behavior. The method is then integrated into topology optimization, resulting in optimized structures that exhibit clear heat conduction paths to the baseplate. Comparisons with high-fidelity thermal simulations demonstrate the effectiveness and efficiency of the proposed method in mitigating overheating in topology optimization.