Wood porosity is of great interest for basic research and applications. one aspect is the cell wall porosity at total dry state. When water is absorbed by wood, the uptake of water within the cell wall leads to a dimension change of the material. A hypothesis for possible structures that hold the water is induced cell wall porosity. nitrogen and krypton physisorption as well as high pressure hydrogen sorption and thermoporosimetry were applied to softwood and hardwood (pine and beech) in dry and wet state for determining surface area and porosity. physisorption is not able to detect pores or surface area within the cell wall. Krypton physisorption shows surface area up 5 times lower than nitrogen with higher accuracy. With high pressure sorption no inaccessible pore volumes were seen at higher pressures. thermoporosimetry was not able to detect mesopores within the hygroscopic water sorption region. Physisorption has to be handled carefully regarding the differences between adsorptives. The absence of water-induced mesopores within the hygroscopic region raise doubts on existing water sorption theories that assume these pore dimensions. When using the term "cell wall porosity", it is important to distinguish between pores on the cell wall surface and pores that exist because of biological structure, as there are no water-induced mesopores present. The finding offers the possibility to renew woodwater-sorption theories because based on the presented results transport of water in the cell wall must be realized by structures lower than two 2 nm. Nanoporous structures in wood at wet state should be investigated more intensively in future. Wood is used for a wide range of applications like furniture, construction components or composites. To increase the usage of wood in products with higher technical requirements (reinforced or functionalized materials), understanding of the basic structure is crucial. Water governs the properties as well as the structure of wood at different climate conditions. Free water molecules from the ambient atmosphere try to gain equilibrium with water molecules in wood cell wall. In the range between 0 and close to 100% relative humidity, water absorption and desorption takes place, leading to different equilibrium moisture contents. The water sorption in this hygroscopic region leads to a deformation of the cell wall, commonly called swelling and shrinking. Therefore the term absorption is used 1. At a certain level, which is individual for each species, saturation of the wooden cell wall with water is reached. Above this so-called fiber saturation point added water remains outside the cell wall, either in the cell lumina or in other biological structures like pits. Wood cell walls contain cellulose, hemicellulose, lignin and various other organic and inorganic molecules, which are characteristic for each species. Despite the knowledge of these compounds, less information is available on the structural organization of all components on molecular level. Hydroxyl groups of cellulose, hemicel...