Because we spend most of our time in enclosed spaces, thermal comfort of buildings rose increasinglyand then energy consumption correspondingly is increased, aggravating the pollution of naturalenvironment. Integrating phase change materials (PCM) into building walls is a potential method ofreducing energy consumption in passively designed buildings. However, there is a strong need forexperimental data to evaluate the capacity of PCM to stabilize the internal environment when there areexternal temperature changes and solar radiations: that is the purpose of our article. The materialtested, a product designed by DuPont and the product looks like a flexible panel of 5mm thickness.The experiments have been carried out with two identical boxes called MICROBAT which dimensionsare (0.62m, 0.62m, 0.62m). In one of the two boxes, the walls are covered with the PCM product. Theexternal temperature is regulated by an air treatment system. The solar radiations are simulated withthe help of spotlights; they enter in the box via the glass faade. The internal and externaltemperatures are measured with radiations shielded thermocouples. The spotlights and the airtreatment system are dynamically controlled, allowing us to simulate the external thermal solicitationsof a day. The comparisons concern the two boxes, one with PCM product and the other one withoutPCM product, submitted to the same thermal solicitations. The results show that the heat storage ofthe PCM covered walls effectively stabilizes the internal environment.