The specific surface area, pore size distribution function, micropore and mesopore volume, and area values have been obtained by gas adsorption/absorption method for various separator materials prepared from polypropylene, cellulose, and poly(vinylidene fluoride). Electrical double-layer capacitors (EDLCs) based on the two identical ideally polarizable nanoporous carbide-derived carbon electrodes and different mesoporous separator materials in 1 M (C2H5)(3)CH3NBF4 acetonitrile solution have been tested by cyclic voltammetry and electrochemical impedance methods. The limits of ideal polarizability, low-frequency limiting capacitance and series resistance, time constant, complex power components, and electrolyte conductivity in the separator matrix have been obtained and discussed. The model of Srinivasan and Weidner [J. Electrochem. Soc., 146, 1650 (1999)] has been modified by introducing into it the very high-frequency constant phase and charge-transfer resistance elements. The applicability limits of the modified model have been tested. Noticeable influence of separator chemical composition, thickness, specific surface area, and pore size distribution on the characteristics of the EDLC single cells have been found.