Sustainable energy conversion systems, such as power electronics and thermal management units, require materials combining lightweight processability with high thermal stability. Silicon carbide (SiC) offers a wide bandgap and high thermal conductivity, while polystyrene (PS) is an easily processable matrix. This work investigates structural and thermal properties of SiC/PS nanocomposites (1–10 wt.% SiC) to identify compositions suitable for energy conversion applications. SiC nanostructures synthesized via carbothermal reduction were incorporated into PS by solution casting. X‑ray diffraction (XRD) with Williamson–Hall analysis assessed structural organization, crystallite size, and microstrain. Thermal behavior was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) under nitrogen at 20 °C/min; degradation kinetics were evaluated by the Coats–Redfern method. XRD confirmed cubic 3C‑SiC, with reflections intensifying with filler content. The 7 % SiC/PS composite exhibited the highest crystallinity (crystallite size ≈ 30.23 nm) and lowest microstrain (ε ≈ 4.18 × 10⁻⁴), indicating a well‑integrated structure. At 10 % loading, significant tensile strain (ε ≈ 1.64 × 10⁻²) appeared, suggesting agglomeration. DSC showed glass transition temperature (T_g) increased from 96.0 °C (pure PS) to a maximum of 117.8 °C at 2 % SiC. TGA revealed that the 7 % composite achieved the highest final degradation temperature (486.5 °C) and optimal thermal endurance. Kinetic analysis demonstrated decreasing activation energy with SiC content (from 288 kJ/mol for pure PS to 194 kJ/mol for 7 % SiC at α = 0.4), while Gibbs free energy remained unchanged, indicating preserved thermodynamic stability despite modified degradation pathways. The 5–7 % SiC/PS composites combine high structural order, minimal microstrain, and superior thermal stability, making them promising candidates for energy conversion systems requiring reliable performance under elevated temperatures, such as power electronic packaging and high‑temperature insulation.