Thermal energy storage (TES) is one method to accumulate thermal energy. In TES, latent heat storage using phase change materials (PCM) has attracted a lot of interest, recently. Phase change slurries (PCS) consist on a carrier fluid binary system composed of water as the continuous phase and micro-encapsulated PCM as the dispersed phase. In this paper, two PCS to be used for TES in buildings were studied: Micronal (R) DS 5007 X, from BASF company, and PCS28, a laboratory made sample. Both samples were characterized using particle size distribution and scanning electron microscopy, to observe the regular spherical microcapsules, the surface morphology, and the wall shell thickness of the microcapsules. Atomic force microscopy was used to analyze the force needed to break the PCS microcapsules, a critical parameter when the PCS are to be used in active pumpable systems, and also to evaluate the effective Young's modulus. Both samples were studied with the microcapsules broken and unbroken. The physicochemical and thermal properties were reported in a previous paper, and it can be concluded that both are proper candidates to be used in TES building heating and cooling applications, but the acrylic shell microcapsules present better breakage resistance to be used in active systems. (C) 2015 Elsevier Ltd. All rights reserved.