Systems, apparatuses, techniques and processes for applying a wet film to a substrate using a slot die are provided. In one form, the air pressure around at least a portion of the discharge end of the slot die is adjustable by the application of a vacuum force in order to control the width and thickness of the wet film being applied to the substrate. In one aspect of this form, the wet film is a narrow, continuous stripe of reagent material applied to a moving web of the substrate from which a plurality of test elements will be obtained. However, different forms and applications are also envisioned.