For the stiffness, there are all sorts of interfacing's from very light to stand on it's own in a hurricane wind. All are washable. For me I use a all cotton, from batting to thread, quilt it stiffly with a close stipple, tie at the corners with a ribbon or narrow cotton "string". That way if I want I can put the whole kit and caboodle in the microwave if I want or just use it on the table. You just make a rectangle to size and pinch up the corners and secure with the ties. It can be unfolded to lay flat if need be, and is certainly very washable. Check out the Pellon website for detailed information on interfacing and a pattern for the insulated carrier. One consideration. Insulbright is not suitable for the microwave, as it has synthetic and metallic fibers in it.