A solution to increase passively the thermal inertia of lightweight wallboard for building envelopes is to incorporate a Phase Change Material (PCM). The thermal mass and thermal conductivity of the panels establish the thermal inertia of the envelope, which causes a damping and time lag of the temperature peaks inside the buildings. The knowledge of the thermal properties of the wallboard is the base of the modeling of buildings, a target uncertainty can be calculated from the modeling purposes. This paper is devoted to the characterization of a panel containing PCM for its thermal properties. Particular attention is devoted to the calculation of the uncertainty of the thermal properties. Commercial microencapsulated paraffin-based PCMs and specific binders have been used to prepare panels. PCMs have been characterized by granulometric and thermo-gravimetric analysis and the porosity of each panel has been determined experimentally by mercury porosimetry. The microstructure of the panels has been observed by SEM analysis in order to recognize the nature of the porous structure. The theoretical effective thermal conductivity of the PCM embedded in the polyurethane resin has been predicted by different models; especially the Maxwell-Eucken and the EMT (Effective Medium Theory) equations just on the basis of the volume fractions and the thermal conductivities of the components. The thermal conductivity estimated with the EMT model closely followed the experimental data measured by thermofluximeter method and the accuracy of the prediction has been analyzed evaluating the uncertainty budget with respect to all the variables of the model. The accuracy of the method resulted to be acceptable for modeling the thermal performance of a building. (C) 2013 Elsevier Ltd. All rights reserved.