Exterior Natural 20 Window Film is an exterior film that goes on the outside of the window, unlike traditional films that are applied on the interior side of the window. These films are made of high quality materials that are designed to weather the elements. The Exterior Natural 20 Window Film works to block heat before it even passes through your windows. This will keep your home much cooler as it reduces the heat stored within the window. The Exterior Natural 20 window film utilizes its low visible light transmittance (20% = Dark) in its black shade to add daytime privacy. Since the film is exposed to the conditions outside, you can seal the edges of the installed film with silicone window caulking after the film has fully dried. This is necessary to increase durability of the film for the outside environment.