Airbag module to protect a vehicle occupant in the event of a collision comprising an expandable bag (11) with gas provided by a generator with, at least, one ventilation orifice (13) sealed with a patch that comprises an elastic membrane (25) destined to be broken as a result of pressure inside the bag (11) to allow gas discharge through the ventilation orifice (13), which is covered with a cover (21) secured to the bag (11) with, at least, one tearable seam (31); hence the opening of the ventilation orifice (13) occurs when the pressure inside the bag (11) is greater than the pressure required to break the membrane (25) plus the additional pressure necessary to tear the seam (31). The invention also comprises a procedure to manufacture the bag.