Can this be used on the outside?

The static cling films are designed for interior use. If the exterior windows were protected from rain, wind etc., it would be fine. There is no adhesive on this film, so there would be nothing to "hold" the film onto the glass. We have an adhesive version of the clear film that may work. It is removable as well. https://www.decorativefilm.com/ultrasafe-260-2-mil-clear-safety-film