When this "hardwall" method of construction is used, the flats can be used repeteadly for longer than the frames covered with muslin. The plywood skin can be taken off and replaced, or other materials, such as vacuum-formed plastic sheets, can be stapled, nailed or glued to the framework. The surface can be painted and papered many times. Hardwall flats also provide a sturdy surface for fastening light fixtures and picture hooks.