Marlen Manufacturing All-flexible Oval Convex Mounting Ring 1-1/2" Opening, 3-3/4" x 2-3/4", Green Neoprene Rubber Marlen Oval Convex All-Flexible Mounting Rings is soft, flexible and completely pliable. It is made of Green Neoprene rubber. Used for persons with fleshier abdomens and short or flush stomas and for stomas located close to the waistline where bending may be an important factor. The convexity applies slight pressure to the stomal area, allowing the stoma to stay within the mounting ring opening and not retract.