An air-bag (1) is provided with a vent aperture (2). A membrane (3) extends across the vent aperture, the membrane defining a smaller aperture (4) than the vent aperture (2). The periphery of the aperture is defined by a thickened part of the membrane. The membrane is formed of an elastic material such as a silicone rubber material. When a very high pressure exists in the air-bag the vent becomes deformed, thus increasing the size of the aperture defined by the membrane, permitting a relatively large flow of air from the air-bag to reduce the pressure within the air-bag.