Abstract The improvement of the thermal and energy efficiency of buildings, regardless of their geographical location, is an objective that needs to be achieved quickly. The objective of this work is to develop a method to evaluate the thermal performance of a hollow block masonry double wall under controlled and pseudo-random experimental conditions. First, the thickness of the air space separating the two walls was varied to see the influence of the gap on this type of wall. Then, this new technology was filled with polystyrene beads to improve the thermal performance at the wall scale. Finally each case studied at wall scale was modeled and simulated numerically in 3D using COMSOL Multiphysics under the same conditions, properties and dimensions as the one tested experimentally. The conclusions confirm that the double wall filled with polystyrene has an excellent thermal behavior compared to the one without the addition of polystyrene beads and that the comparison between numerical and experimental results gave very satisfactory results.