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The bark-water relation and the moisture transport in bark are essential for the living tree but also for the industrial utilization of bark. Thus the bark-water relation of beech (Fagus sylvatica ) and spruce (Picea abies ) have been studied in the present work. The sorption isotherms were determined at 35°C for both wood and bark and the water diffusivity was measured under steady state conditions (cup method) and under unsteady state conditions, i.e. via sorption test. The sorption isotherms were calculated based on the Hailwood-Horrobin (HH) model. It was observed that beech wood and bark have a similar hygroscopic behavior, whereas spruce bark is more hygroscopic than spruce wood in all the relative humidity (RH) ranges. The radial diffusivity was in the range 1.2 ⋅ 10-11-2.2 ⋅ 10-11 m² s-1 for spruce and beech bark, respectively, when the driving force of the diffusion is the gradient of bound water. [ABSTRACT FROM AUTHOR]