Applied on the outside of the building, BuyDecorativeFilm's EXS15 Exterior Daytime Privacy and Sun Control Silver 15 Window Film works to block heat before it even passes through your windows. Therefore, the EXS15 helps keep your home much cooler as it reduces the heat stored within the window more than traditional window films that are applied on the inside. Along with high heat rejection, the Exterior Silver 15 also provides great daytime privacy with its reflective surface, creating a one way mirror during the day only. 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.