A rack panel is a flat piece of metal that attaches to the front (or less frequently, to the rear) threaded bars of a rack with rackscrews. They come in a various heights to fill the needed number of "U" spaces. Rack Panels come in a variety of formats. Some are vented (have holes in them) for circulation. Some have hinges to allow access inside the rack. And some are blank. Blank panels are available in a variety of finishes. More than just filling unsightly unused positions in your rack, rack panels can improve ventilation, allow or restrict (as desired) access inside the rack, and structurally strengthen the rack by their mere presence.