Microencapsulated phase change materials (MPCM) enclose the core material  inside the shell, providing higher thermal regulation performance by expanding the heat transfer surface and preventing the leakage of core materials. This study adopted sol–gel methodology to synthesize Paraffin@SiO2 to enhance the latent heat storage capacity. The same is implemented in different doses to study their thermal gradient performance in ambient cured fly ash–Ground Granulated Blast Furnace slag (4:1) alkali geopolymer (Gp). The liquid migration test results proved the outstanding tightness of paraffin in the MPCM capsule. Though adding MPCM has slightly reduced the compressive strength, no significant characteristic changes are observed in IR reflection. This confirmed the integration of MPCM in a geopolymeric binder. The heat flow and internal temperature were measured from the thermal test conducted on a geopolymer panel to evaluate the effectiveness of PCM. Compared to the neat PCM, the composites demonstrated high thermal performance with a decrease in indoor temperature up to 3–4 ℃. It is attributed to the latent heat capacity and thermal stability of the MPCM, as derived from the DSC test results. To conclude, this finding demonstrates that eco-friendly geopolymers effectively increase the thermal inertia and reduce energy consumption in buildings.