The cross-sectional shape of a fiber has an effect on the comfort-related fluid transfer properties of a fabric, such as wicking, moisture transfer, and tactile properties. For analysis of these properties via simulation, an equation for the hydraulic pore size was derived on the basis of a structural model. The major variables considered in the equation were the fiber shape factor, the fiber fineness, and the mass density of the fibrous assemblies. Using the pore size from the equation, the permeability and the capillary pressure were calculated and then the horizontal and vertical wicking behaviors, i.e., time dependent activity, were simulated. The results show that the equation can be used to quantitatively analyze the fluid transfer properties in terms of the fiber shape factor, which can provide useful information in designing a fiber structure for improving comfort properties.