An active bolster for an automotive vehicle has a outer trim panel with a welding track. An expandable bladder member has a central section configured to attach to a support structure of a vehicle, a welding flange along a peripheral edge, and a pleated region between the central section and the welding flange. The welding track and the welding flange are joined by a hot weld to form a sealed chamber. The welding track includes a plurality of radially-spaced stepped pits. Each pit has an upper section defining a first opening with a respective first cross-sectional area and a lower section defining a second opening with a respective second cross-sectional area smaller than the respective first area. A perimeter of each upper section is melted by the hot weld and a perimeter of each lower section is not melted by the hot weld.