Airbag module for protecting an occupant of car with a bag (11) that includes a main front panel (17) and main rear panel (19) connected by its ends and a retention band (21) connected to the panels in two opposite ends (31, 33), capable of withstanding maximum pressure during the unfolding of the bag (11) without breaking or disconnecting from said panels, and whose length L is less than the maximum distance D that would exist between said opposite areas (31, 33) during the unfolding of the bag should said retention band (21) not exist; the bag has a ventilation orifice (23) around one of the union areas (31, 33) that can be covered by the main front and rear panels (17, 19) when the bag (11) contacts the occupant (15).