New processes and apparatus for forming lap seams and making prefastened disposable absorbent articles are disclosed. The apparatus can include an interior folding mechanism adapted to position a first panel in an interior position and an exterior folding mechanism adapted to position a second panel in an exterior position relative to the interior position. The interior folding mechanism can include a mandrel defining a curved peripheral surface and an interior forming shoulder in proximity to the mandrel. A fluid pressure device can establish an air flow between the mandrel and the interior forming shoulder. The forming shoulder can modify the direction of the air flow as the first panel travels in a machine direction to increasingly fold the panel over the curved peripheral surface.