In this study, changes in the hygroscopic properties of two main wood species for violin making, Norway spruce and sycamore, after treatment with Physisporinus vitreus and Xylaria longipes were investigated. Swelling and moisture sorption capacity of wood at the growth ring scale were visually and quantitatively assessed by thermal neutron radiography analysis. It was demonstrated that the fungal treatment improved the dimensional stability of both Norway spruce and sycamore, but also increased their moisture adsorption capacity. Dynamic vapor sorption tests and measurements of the changes in dimensions of the specimens in the laboratory were in good agreement with the results of neutron radiography analysis. The main difference between the moisture sorption of the untreated controls and treated wood was observed at high relative humidity, e.g., above 75%. The contradictory behavior of the increased hygroscopicity and reduced swelling was explained by selective degradation of the chemical components and condensation of the moisture content gained in the capillary voids that developed in the cell walls during fungal decay
