The swelling/shrinkage of spruce wood samples (Picea Abies) is documented with high resolution XRay Tomography and advanced image analysis tools. We report the reversible moisture-induced global and local deformations at the cellular and sub-cellular scales. In particular, we present sophisticated methods for detecting local deformations in the cell wall. Insight is given on the hygromechanical behaviour of wood cell material and on the role of ultra-cellular components in wood, such as bordered pits and rays