An active bolster for an automotive vehicle has base wall for mounting against a rigid structure of the vehicle. A front wall overlies the base wall and forms an interior trim piece of the vehicle. The base wall has a first surface facing the front wall, and the front wall has a second surface facing the base wall. The base wall and front wall are joined around a closed perimeter to form an inflatable bladder with an initial open space between the first and second surfaces. The base wall includes a wide rib projecting from the first surface continuously along the closed perimeter, the wide rib having a minimum radial width along the closed perimeter equal to a first predetermined radial width. The front wall includes a plurality of narrow ribs projecting concentrically from the second surface continuously along the closed perimeter. Each narrow rib is welded to the wide rib, and each narrow rib has a respective radial width at each respective location along the closed perimeter less than half the radial width of the wide rib at the respective location.