Airbag with adaptive ventilation device

Gas bag (1) for protecting a vehicle occupant with at least two in the edge region interconnected layers of material (3), which include at least one fillable with a gas shielding chamber, - the gas bag (1) has a ventilation device with a field (5, 15) of ventilation holes (6, 16), - which cooperates with an elastic element such that its effective area is a protective chamber, at least in dependence on the respectively acting pressure in the gas, - said box (5, 15) of ventilation holes (6, 16) is closed at rest and with relatively low gas pressure in the protective chamber by a cover, - wherein the cover is connected with the elastic member, so that with increasing gas pressure, the cover member is slidable and the pitch (5, 15) of ventilation holes (6, 16) at least partially exposing, and - wherein the elastic member is formed as a retaining band (7, 17) which with its first and second ends (8, 9, 18, ...