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• Hygrothermal and mechanical properties of a recycled expanded polystyrene-based material have been assessed. • Sorption isotherm curves of expanded polystyrene mortar exhibit hysteresis phenomenon and show a low water vapor adsorption. • Thermal conductivity and specific heat capacity are highly dependent of temperature and water content. • Water vapor permeability coefficient increases with polystyrene incorporation because of air bubbles appearance. The construction sector is the most energy consuming one in the world, and it has a significant ecological impact. Indeed, concrete manufacturing overuses natural resources such as sand or gravel, and the need to use alternative building materials is urgent. Choosing adequate building materials takes an important part in the success of a high environmental quality project. This suggests using new alternative solutions, based on recycled materials or waste. However, their use being relatively recent, these materials properties are not widely known and there is lack of information concerning their hygrothermal and mechanical behavior. In this context, the present work aims then to highlight the experimental characterization of hygric, thermal, physical and mechanical properties of a recycled expanded polystyrene mortar, which is a relatively new building material, generally used for its thermal performances. Indeed, a complete characterization campaign was elaborated in this work, allowing a precise determination of the main properties of the material. The experimental characterization also included a usual cement paste made of the same cement as a reference material, in order to evaluate the polystyrene adding impact on the measured hygrothermal properties. Different methods of sorption isotherms determination were presented, and a better attention was devoted to the sorption hysteresis phenomenon characterization. The macroscopic hygrothermal properties, such as water vapor permeability, thermal conductivity and thermal capacity were also investigated function of the temperature and water content evolution. Mechanical strength was also determined, and SEM observations were performed to study the morphology of the material. Experimental results show that expanded polystyrene mortar exhibits a good thermal conductivity and thermal capacity, and a higher water vapor permeability. These results provide data for better forecast on the prediction of the hygrothermal and mechanical behavior of such material. [ABSTRACT FROM AUTHOR]