A mask system to deliver a flow of air at a positive pressure with respect to ambient air pressure to an entrance to the patient's airways includes a frame and a cushion forming a plenum chamber. The mask system includes a mask vent including an exterior recess positioned outside the plenum chamber and including a bottom surface, a plurality of vent holes each including a vent inlet and a vent outlet, and a plurality of ribs extending from the bottom surface. The plurality of ribs includes at least a first rib and a second rib, the first rib having a free end spaced apart from a free end of the second rib, and the first rib or the second rib is positioned between the first vent outlet and the second vent outlet.