A covering for an architectural opening that includes a plurality of flexible slat materials overlapped and joined along longitudinal edges resulting in a continuous roll-up covering material. The covering includes a first fabric material including an inner surface, an outer surface, a top end, and a bottom end, the bottom end of the first fabric material being folded over to define a first folded piece of fabric; a second fabric material including an inner surface, an outer surface, a top end and a bottom end; and a stiffener positioned between the first folded piece of fabric and the second fabric material along the top end of the second fabric material, an inner surface of the stiffener being adhered to the outer surface of the second fabric and an outer surface of the stiffener being adhered to the first folded piece of fabric.