An apparatus for helping to protect an occupant of a vehicle comprises an airbag having a primary chamber and a secondary chamber. The primary chamber has a stored condition and is inflatable to a deployed condition to cover a portion of the vehicle. The secondary chamber has a stored condition and is inflatable to a deployed condition to cover portions of the vehicle left uncovered by the primary chamber. At least one passive vent provides fluid communication between the primary and secondary chambers. At least one active vent is actuatable to provide fluid communication between the primary and secondary chambers. An inflator is actuatable to provide inflation fluid to the primary chamber. The at least one passive vent directs inflation fluid from the primary chamber into the secondary chamber. The at least one active vent is actuatable to direct inflation fluid from the primary chamber to the secondary chamber.