<p>Polycarbonate (PC) is a promising candidate for use as a porous resin, but its heat resistance must be improved to broaden its applicability. Such improvement could be achieved by controlling the crystallinity and porosity of PC through foaming with a supercritical gas. This study investigated the effects of supercritical CO₂ treatment on the crystallization, porosity formation, and thermal stability of PCs with varying complex viscosity. After treatment, all PC samples exhibited opacity, which was attributed to either induced crystallization or pore formation. Differential scanning calorimetry revealed the progression in crystallization, with the estimated crystallinity decreasing with complex viscosity. Microscopic analysis confirmed the changes in pore size and distribution depending on the complex viscosity, with lower-complex-viscosity samples forming larger pores. Density measurements indicated that the porosity formation-induced density reduction outweighed the density increase induced by crystallization. Thermal stability tests revealed pore retention up to 200&#xa0;°C, highlighting the potential of porous PC materials processed with supercritical CO₂ for thermal applications.</p> Graphical abstract <p></p>