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This paper is devoted to the measurement and analysis of the mass transfer properties in the hygroscopic range of wood specimens of poplar (Populus robusta) before and after a treatment at 200 C. In this work, two different properties have been determined on the same samples: the mass diffusivity (property of mass migration under the effect of a concentration gradient) and the air permeability (property of mass migration under the effect of a pressure gradient). These properties are very important to evaluate the potential usage of thermally treated products in the packaging sector, because they define gas and water vapour transfer. The experimental data prove that the thermal treatment reduces the value of mass diffusivity probably due to the chemical modification of the cell wall. However, the permeability value does not change significantly, probably because the thermal treatment has a slight impact on the porous structure of wood.