Geopolymer foams are lightweight, porous materials increasingly recognized for their potential in sustainable construction, owing to their low density, tunable porosity, fire resistance, and environmentally friendly synthesis. Despite these advantages, their inherent thermal storage capability is relatively limited, which restricts their performance in applications where energy efficiency and thermal regulation are critical. To overcome this drawback, the present study focuses on the development of geopolymer foams enhanced with paraffin-based phase change materials (PCMs) encapsulated within diatomite. Diatomite, a naturally occurring siliceous material with a high surface area and porous structure, serves as an effective carrier for paraffin, ensuring good retention and reducing the risk of leakage during repeated melting and solidification cycles. The modified foams were prepared through the incorporation of diatomite-encapsulated PCM into the geopolymer matrix during the foaming process. Comprehensive characterization was carried out to evaluate the structural, thermal, and mechanical properties of the resulting composites. Scanning electron microscopy confirmed the successful distribution of PCM-loaded diatomite within the pore structure. At the same time, specific heat measurements highlighted a marked improvement in latent heat storage capacity without significant loss of insulating properties. Moreover, mechanical tests indicated that the addition of encapsulated PCM did not compromise the structural stability of the foams, maintaining adequate compressive strength for potential building applications. The results of this study demonstrate that integrating diatomite-encapsulated paraffin PCM into geopolymer foams provides a multifunctional material that combines thermal insulation with enhanced energy storage capacity. Such composites are particularly promising for applications in energy-efficient buildings, where passive thermal regulation and reduced energy consumption are increasingly important. Overall, the findings underscore the potential of geopolymer foams as sustainable construction materials with improved thermal management capabilities, contributing to the broader goals of energy conservation and environmental protection.