An airbag system for a vehicle includes an airbag having a vent and a vent cover configured to close the vent, an actuator, and a tether. The tether is connected between the actuator and the airbag. The vent cover is positioned outside the airbag and between the tether and the airbag. During inflation of the airbag but prior to activation of the actuator, the tether is in tension so as to apply a normal force against the vent cover to maintain the vent in a closed state. The actuator is configured to be activated to reduce or release tension in the tether to reduce the normal force applied by the tether to the vent cover and allow inflation gas to move the vent cover to place the vent in an open state.