Rev-A-Shelf Fillers revolutionized otherwise wasted space in your kitchen. Normally a "filler" or extra space is simply covered up with a decorative front for either your wall (upper) or base (lower) cabinets, but with the Rev-A-Shelf line of fillers, it turns that otherwise wasted space into usable space. Fillers are intended to be installed in-between (2) cabinets in new kitchen cabinet construction and will not work in existing kitchen cabinets. Fillers are available in different widths and heights (always good to consult with a kitchen designer to incorporate into your new kitchen).