Poly(vinyl pyrrolidone) tracers are used to investigate the porosity variation on ion-exchange materials. The porosity was measured as a function of the salt concentration in the mobile phase and of the amount of protein adsorbed on the material. Immunoglobulin G (IgG) and human serum albumin (HSA) are selected as proteins. Two materials with different pore size distributions were investigated. The surface of both resins is functionalized with tentacles that carry a terminal ionic group. In both materials, a small increase of the accessible porosity was observed for increasing salt concentrations. A larger effect was observed in the presence of protein adsorption. The accessible porosity decreases quickly as the amount of adsorbed proteins increases. The decrease in porosity due to the HSA adsorption is smaller than the decrease caused by IgG.