Here at Pro Cut Signs we get more questions about the application of vinyl to glass and the problems with it Applying vinyl to glass is one of the most challenging parts in vinyl application. The glass MUST be free of ANY contaminants, including sap, road grime, wax, or any windshield treatments that are commonly used. Rain-X products are especially difficult to remove. Most contain silicone or silicone based products which interfere with adhesion to the glass. Another problem that crops up a lot from beginners is the use of glass cleaners with ammonia to clean the glass. The ammonia interferes with the adhesive and will cause it to fail and should NEVER be used by the beginner. We here at Pro Cut Signs use isopropyl (rubbing) alcohol with at least a 90% mix and a razor blade to make sure everything is removed. We then use an application fluid to help us position it on the glass.