We present a thorough characterization of the thermal properties and thermal reliability of the eutectic mixture of decanoic acid with tetradecanoic acid, as a phase change material (PCM) of potential interest for passive temperature control in buildings. From the temperature-composition binary phase diagram we found that the eutectic composition is 0.82 +/- 0.02 mole fraction (78 +/- 2 mass%) decanoic acid. We thoroughly characterized the thermal properties of the eutectic mixture. The eutectic composition has a high latent heat of fusion Delta H-fus = 153 +/- 15 J g(-1) and a melting temperature T-onset = 20.5 +/- 1.5 degrees C. The heat capacity measured as a function of temperature for the solid and liquid phases just below and above the melting point is 1.9 and 2.1 +/- 0.2 J K-1 g(-1), respectively. The average value of the thermal conductivity of the solid phase measured between -33 and 9 degrees C is kappa(s) = 0.20 +/- 0.02 W m(-1) K-1 and for the liquid phase, the thermal conductivity is kappa(l) = 0.23 +/- 0.03 W m(-1) K-1 for 28 and 38 degrees C. The mixture has a good long-term thermal stability as indicated by negligible changes in Delta H-fus and T-onset after 3000 melt-freeze cycles. The parameters determined in this work allow more accurate modeling and optimization of the behavior of the eutectic mixture in preparation for implementation as a thermal energy storage PCM. (C) 2016 Elsevier Ltd. All rights reserved.