Disclosed are embodiments of apparatus, methods, and systems for automatically closing a vent opening in response to inflation of an airbag cushion. In some embodiments, primary and secondary tethers are provided, both of which are coupled to an airbag cushion. The primary tether may be used to restrain the inflation size of the airbag cushion during a partial deployment. A tether cutter may also be provided to cut the primary tether upon detecting a condition that would warrant full deployment of the airbag cushion. The secondary tether may be configured to at least partially close one or more vent openings in response to the airbag cushion being inflated to a fully-inflated configuration after the primary tether has been cut.