A building materials' properties have a great influence on its energy performance, and this is particularly true of the hygrothermal properties of the insulation material. The variation in moisture content generated by weather conditions can have a strong impact on heat transport. The phenomena involved are very complex and difficult to fully simulate numerically, particularly when the moisture variation occurs under exposure to rain. In the case of the medium density expanded cork agglomerate that is increasingly used without any coating as an external thermal insulation layer of buildings, these phenomena can be particularly relevant. Thus, this paper evaluates the importance of varying moisture content on the thermal behavior of a wall covered with uncoated medium density cork agglomerate when exposed to rain. A simple analytical model that simulates the heat transfer phenomenon was used to quantify its importance by comparing the mathematical results with those obtained experimentally. Steady and unsteady state conditions were simulated. For comparison purposes, winter and summer environmental conditions for both dry and wet weather were assumed. The results show that the thermal behavior of the wall is only affected in the rainy period, until the first few hours when the expanded cork board starts to dry. When rain is simulated, the temperature of the water has a key effect on the wall's behavior. The moisture transport phenomenon and changes in the hygrothermal material properties are almost entirely confined to the upper layers of expanded cork board and to the rainy period. (C) 2018 Elsevier B.V. All rights reserved.