The changes in the interaction of wood with liquid water caused by thermal modification (TM), which is a less studied effect of TM, was investigated. Birch (Betula spp.) wood and pine (Pinus sylvestris L.) sapwood were thermally modified and their properties compared with unmodified counterparts. The wettability was assessed by sessile drop contact angle measurements. The water permeability was measured by capillary absorption tests through the radial and tangential surfaces and indirectly evaluated from water distribution in cross-section of boards exposed on weathering rack to an intensive rain episode. The liability to rapid drying was evaluated by comparing the amount of the retained water in impregnated specimens after definite time period of drying in controlled environment. For both woods, TM caused not only a reduction in wettability, but also a reduction in drying rate, which could result in prolonged periods of high wetness during service. Lower liquid water permeability was observed for TM birch through both lateral surfaces which was supported by the results of water distribution in boards exposed to rain. Significant increase in water absorption was detected for TM pine through tangential surface in both tests used for evaluating water permeability of wood.