The extent of dissolution and polymerization/polycondensation of metakaolin added biomass to alkaline solution was exploited to design highly porous insulating geopolymers using sodium polyacrylate and calcium silicate to enhance their hygroscopic properties. 2.5 to 7.5 wt % of sodium polyacrylate and 20–40 wt % of calcium silicate efficiently embedded into the geopolymer gel were able to increase the absorption and desorption capacities between 30 and 50% while maintaining the thermal conductivity at 0.13–0.16 W m−1K−1 at 70% of relative humidity and 0.22–0.28 W m−1K−1 when the relative humidity is above 80%. The extension of the reactivity of metakaolin added biomass results to a homogeneous gel with improved specific surface area which enhances the hygrothermal properties. The pore size (essentially nano and meso) and their interconnectivity make the obtained porous matrices promising candidates for core vacuum insulation and regulation of the thermal comfort for Net zero Energy buildings. A Machine Learning (ML) method, the polynomial regression, was used to ascertain the close correlation between the thermal conductivity, temperature, moisture absorption and time. Also, the increase in the amount of nano and meso pores increases the tortuosity of the porous matrices and explain the improvement of the hygrothermal properties. The changes in the microstructure with the increase of the volume of fine pores was found to be suitable for hygrothermal behavior (absorption-desorption).