In this study, we synthesized polymer composites by incorporating polyhedral oligomeric silsesquioxane (POSS) units into polythiophene to reduce the thermal conductivity of conductive polymers. The synthesized polymers were copolymers with various POSS incorporation rates, reflecting the monomer feed ratios. Introduction of POSS units proved highly effective in reducing the thermal conductivity of the polymer films by more than half and improving the Seebeck coefficient, although it markedly reduced the electrical conductivity. This composite approach shows promise in reducing the thermal conductivity of conductive polymers, suggesting the need for further research to improve electrical conductivity.