This study presents experimental research on the mechanical and physical properties of unsaturated polyester composites before and after reinforcement. The study involved the preparation of hybrid composite materials from a polyester matrix with 5% each of chopped glass fibers and chopped carbon fibers. Silicon carbide nanopowder was then added at varying weight percentages (0%, 1%, 2%, and 3%). The study also included testing several mechanical properties, including tensile strength, modulus of tensile elasticity, impact resistance, and stiffness, for all samples. The thermal conductivity of the samples was also calculated. The results showed an improvement in tensile strength, impact resistance, stiffness, and modulus of tensile elasticity with the addition of silicon carbide nanopowder. An increase in thermal conductivity was also observed in the samples compared to the pure unsaturated polyester sample. Sample (D) exhibited the highest values in mechanical properties, while the unreinforced pure polyester (PUE) sample recorded the lowest. Regarding thermal conductivity, sample (C) recorded the highest value compared to the pure unreinforced polyester (UPE) sample, while the unreinforced pure polyester (UPE) sample recorded the lowest. These results indicate that polymer composites reinforced with more than one type of fiber, in addition to nanoparticles, improve the mechanical and thermal properties of polymer composites used in the manufacture of tools or structures in various applications, particularly those exposed to external factors and environmental conditions