The thermal performances of a PCM copolymer composite wallboard has been experimentally investigated in a full scale test room. The test cell is totally controlled so that a typical day can be repeated (temperature and solar radiative flux). Effects of the PCM are investigated comparing the results obtained with and without composite wallboards for three cases: a summer day, a winter day and a mid-season day. The results show that: (1) for all the cases tested, the decrement factor varies between 0.73 and 0.78 which is quite interesting for use in buildings and particularly for renovation; (2) the air temperature in the room with PCM lowers up to 4.2 degrees C, the comfort enhancement is more important if the surface temperatures are also considered; (3) the PCM wallboards enhance the natural convection in the room and then there is no thermal stratification contrary to the room without composite; (4) the numerical experiments are fully described and can then be used to evaluate PCM numerical modeling. (C) 2009 Elsevier Ltd. All rights reserved.