Window Film is a polyester product typically made of Polyethylene Terephthalate (PET). Most films are applied to the interior surface of a glass window in a home, commercial buildings or car; they also have a scratch resistant coating on the outer surface to protect the film.
There are many types of window films. Some are clear and feature multiple layers of PET to offer protection from shattering glass; others are tinted with metals, dyes, or pigments to reduce the visible light transmitted through the glass, and block heat coming through from the sun. There are even decorative window films that can replicate the look of frosted glass or etched patterns.