Abstract: Embodiments of the invention include a unidirectional exhalation valve for a respiratory device such as a facemask. The valve opens to vent air out of the interior of the facemask and closes to prevent the inflow of ambient air. The valve is comprised of a valve body, a valve cover and a membrane. The membrane is secured to the valve body around its perimeter by the valve cover. The membrane is comprised of two or more flaps that flex toward a central region, in a direction away from the valve body, to open the unidirectional valve.