Cellular concrete is an alternative to conventional concrete as a low-density and high-insulating building material. The eco-cellular concretes (ECCs) based on geopolymer technology have been recently introduced by the scientific community. A form of ECC was studied, in which the fluid catalytic cracking residue and the blast furnace slag were employed as precursors, the rice husk ash was utilized as an alternative silica source in the activator, and the aerating reagent was replaced with recycled aluminum foil. Field emission scanning electron microscopy, optical microscopy, and ImageJ version 1.48 software (National Institutes of Health) were employed to characterize the void distribution. Bulk density and porosity were determined by hydric tests. The results revealed that lowest densities without strength loss were obtained when the cementing matrix had a homogeneous void system: similar spacing between pores, narrow size ranges, and nonconnected pores. A relationship was established between open and closed porosity with density and thermal conductivity.