Fourth line of logPerm around 0 log units relates to an unrestrained diffusion in water and represents the maximum permeability measurable by experimental methods in water medium. Such logPerm values correspond to the permeation of molecules through water slice of similar thickness to membrane, where there is no energy barrier for permeation and diffusion coefficient is equal to the water self-diffusion coefficient. Then, the homogeneous solubility model for the permeation coefficient is valid: