A method is presented by which estimates can be made on swelling, bulk modulus, and internal stresses in gel materials as related to water sorption. Porous gel materials are considered as gel materials made porous by capillary pores large enough not to create capillary condensation and capillary tension.Experiments made at the Department of Structural Engineering and Materials, indicate that a number of cellulosic materials can be considered a porous gel materials. Sorption analysis show that water taken up from ambient relative humidity by pulp, for example, cannot by far be explained only by surface adsorption. Volumetric sorption as in gel is very likely to be the main sorption mechanism in the whole area of ambient relative vapor pressures from 0 to very close to 100%. Capillary pores in pulp are first saturated with water when pulp is placed in bulk water. The results might be of interest in further studies of cellulosic materials, especially such studies where main topics are mechanical behaviour.