Large thermal mass is an important physical property of a building. It plays significant role in decreasing the amplitude of internal air temperature swings caused by the weather circumstances. By this the energy consumptions of the buildings can be reduced both by decreasing heating and decreasing cooling demand. So it is easier to provide the human comfort with less usage of engineering equipment. Nowadays energy saving is relevant because of the energy price increasing due to resources of the fossil fuels are exhausting. The thermal mass depends on the specific heat and the density of the material. The phase change materials (PCMs) are a modern way to increase the thermal mass of the building since it uses the latent heat of the materials instead of the heavy mass. This technology is suitable for providing high thermal mass to building with light construction. The application of PCMs in building materials is in evolving phase. The results about these products are very promising. But the application in wide range of it requires more effort. This thesis is aimed at testing a prototype gypsum board with PCM encapsulation manufactured by BASF and a development of a new lab for further ESES student in SERC. The test was executed with two boxes, one built with this special gypsum board and one with conventional gypsum board. The test based on a theoretical part and a measurement part with the same environment; open air and laboratory location. The theoretical model well covers the measured result, showing that the special gypsum board has the expected effect on the air temperature.