Abstract: The invention relates to an airbag comprising an inflatable cushion (11) with the gas produced by a generator when a collisions occurs having a vent hole (13) made in the inflatable cushion (11) which is provided with a device (21) including a part (23) made of flexible material with at least one hole (25) fixed to the inside of the inflatable cushion (11) and incorporating means for allowing the separation thereof from the cushion (11) when the internal pressure in the cushion is lower than a predetermined limit (Pt) preventing it from closing the vent hole (13) and stop doing so when the internal pressure in the cushion (11) exceeds said predetermined limit (Pt) such that it completely or partially closes the vent hole (13) when it adheres to the cushion (11) due to the effect of the pressure.