The examined flours were characterized by variable chemical composition resulting from the genetic variety. The semolina (hard wheat flour) and farina (soft wheat flour) sorption isotherms were determined with the use of the static-dessicatory method at 20°C. The equilibrium water content significantly depended on the product type and water activity. A distinct increase of the water content was found in both examined types of flours at aw about 0.75. Probably above the level of aw = 0.75 there appeared the phenomenon of capillary condensation. On the basis of the BET equation there was determined the capacity of a monolayer (semolina - 5.53 and farina - 5.88 g×(100 g.s.s)-1) and on its basis the specific surface of sorption (semolina - 194.2 and farina - 206.6 m2 g-1). There was also determined the general capacity of capillaries in the area of capillary condensation, recording higher values of this parameter for farina. On the basis of Kelvin equation the structure of examined flours was identified, defining the most probable radius of capillaries and indicating the radius of capillaries which are filled in the initial phase of condensation.