This is a 3 x 4' roll of Black-Out Cling Vinyl from Delta 1. It is used to eliminate any ambient light is not desired such as in a darkroom. This is a 12 mil thick vinyl material that clings to glass or plastic but leaves no residue when it is removed. It can be trimmed to size to fit windows and is reusable. It is recommended that the surface it is applied to be thoroughly cleaned with mist water. If the weather is cold, tape may be required to hold the vinyl in place.