Hollow concrete blocks can be thermally improved either by modifying their cavities shapes or by adding insulation materials into these cavities. It is also possible to improve the thermal conductivity of solid concrete matrix by incorporating some materials to its composition like recycled solid wastes for example. This paper offers a solid and comprehensive study for thermally improved hollow blocks through a case study from the Lebanese context and provides a scientific basis for improving the thermal performance of these blocks. The effect of adding expanded polystyrene (EPS) beads to the concrete solid mixture was investigated in this study through numerical and experimental approaches. The experimental and numerical results were in good agreement and the potential thermal improvement by adding EPS beads to concrete mixture was examined on both numerical and experimental levels. The numerical results for the three-dimensional (3D) model allow the visualization of the heat flux and temperature distribution in the block as well as the air velocity and convective heat exchanges inside the cavities of the block. The results showed that the block thermal resistance can almost double by adding 18 g of polystyrene beads to the concrete mixture.