a) Experimental situation: one side of the membrane is subjected to a flow of dry air, while the other is subjected to a flow of humid air. Relative humidity is varied in the range [~20%–~90%]. The water profiles measured by MRI b) are recorded in the steady-state regime for each air humidity condition. c) Water flux measured through the membrane from the wet to the dry side. d) Evolution of the total interface resistance R_int, the constant resistance due to boundary layer effects (R_boundary) and the interfacial resistance due to membrane surface morphology R_skin as a function of the air humidity imposed on the wet side.