A side airbag comprises a first side, a second side, a main portion and an extension portion. The main portion has a recess in the first side. The extension portion is supported by and is in communication with the main portion. A first tether is between the main portion and the extension portion. A vent is disposed in the main portion and selectively is moveable from a closed orientation to an open orientation. A second tether extends from the second side to the recess.