A WVT unit for a fuel cell system that employs a spiral-wound design to reduce its size and increase its performance. The WVT unit includes a center tube having a plurality of openings through which the cathode exhaust gas flows. The WVT unit also includes a cylindrical portion wound around the center tube that includes a plurality of enclosures and a plurality of dry spacer layers separating the enclosures. Each enclosure includes a pair of membranes separated by a wet spacer layer. The dry cathode inlet air flows down the dry spacer layers between the enclosures and the cathode exhaust gas flows into the plurality of enclosures through the openings in the center tube along the wet spacer layers to allow the membranes to absorb humidification that is transferred to the cathode inlet air.