Thermal Insulation Properties and Stability of Hybrid Epoxy Composites Reinforced With Palm Kernel Shell and Bilinga (Nauclea diderrichii) Sawdust

Thermal resistance is a critical factor for indoor comfort, as materials with poor insulation permit external heat penetration, thereby increasing cooling demands and operational energy costs. Thermal insulation materials are essential for reducing heat transfer and improving energy efficiency in buildings, particularly in tropical regions. This study investigates hybrid epoxy composites reinforced with NaOH‐treated palm kernel shell (PKS) and Bilinga sawdust, aimed at developing a low‐cost, thermally stable bio‐composite. Composites were fabricated at filler ratios of 20/40, 25/35, and 30/30 wt.% using a DGEBA epoxy matrix and evaluated for thermal effusivity, volumetric heat capacity, thermal conductivity, and thermogravimetric stability. The hybrid formulation achieved thermal conductivities of 0.075–0.099 W·m −1 ·K −1 , notably lower than values commonly reported for natural‐fibre epoxy systems (0.10–0.15 W·m −1 ·K −1 ). TGA revealed T onset values up to 265°C and char residues of 17.25%, representing a 10°C–15°C improvement and higher char yield compared with typical untreated or single‐filler epoxy composites. These findings confirm that combining lignin‐rich PKS with cellulose‐rich Bilinga produces a synergistic enhancement in insulation and thermal stability. Overall, the hybrid system demonstrates a ∼60%–70% reduction in thermal conductivity relative to neat epoxy, highlighting its strong potential for sustainable thermal‐insulation applications in building materials.