An airbag cushion is disclosed for use in automotive protective systems. The airbag cushion includes a vent flap that, prior to cushion deployment, extends from the cushion exterior through a vent. A strap is coupled to the vent flap and to an interior surface of the cushion. Upon airbag deployment, the strap extends until taut or extends until the cushion encounters an obstruction. If pulled taut, the strap pulls the vent flap into the cushion interior where the interior air pressure effectively presses the vent flap against the vent. If the cushion encounters an obstruction, the strap remains lax, and the vent remains open. Devices are provided for retaining the vent in the closed position during occupant ride down.