An active bolster for a vehicle is provided, wherein the bolster comprises an expansible hollow interior that is inflatable and is self-supporting in both an inflated and in an uninflated position. The bolster has an inflator module for inflating the expansible hollow interior. The bolster has an inner wall for projecting inwardly into the vehicle and away from the side of the vehicle on inflation of the expansible hollow interior. The bolster may have a relatively non-expansible component located between a first expansible chamber and a second expansible chamber. The bolster may comprise an outer wall having an attachment portion for attaching the outer wall to a portion of the side of the vehicle.