A vacuum-forming system for deforming a forming blank is disclosed. The system includes a tool and at least one regulator bag disposed adjacent to the tool. The regulator bag includes a sealed bag having an exterior and an interior and a first volume and a defined passage from the interior to the exterior of the regulator bag. The passage is configured such that the regulator bag has a rate of deflation wherein the sealed bag will deflate from the first volume to a second volume over a determined period of time while the exterior of the sealed bag is at a determined reduced pressure. The system also includes a vacuum membrane coupled to the tool, the membrane configured to form a vacuum space enclosing the forming blank and the at least one regulator bag.