Almost everyone has seen window film that has turned purple from exposure to the sun. However, many people, even many in the industry, do not know why window film turns purple.

First, let’s discuss what is happening that changes the film to a purple color. For this, I am going to need all of you to think back to when we all learned about primary colors and the color spectrum in grade school. The three primary colors are red, blue and yellow. All colors in the spectrum come from a combination of these three colors. A complete absence of any primary color will give you absolute white, and a combination of equal parts all three primary colors will give you absolute black. As you can see in the picture, purple is primarily a combination of the red and blue primary colors.

As mentioned above, all colors are derived from a mixture of the three primary colors. The window film you use, whether it is smoke, charcoal, neutral, etc., has the color derived from a mixture of these three primary colored dyes. While all three of the primary colors are susceptible to fading from the sun, yellow typically will fade at a faster rate than blue or red. So, if you are following along, you can guess what happens next. As the film is exposed to sun and the yellow dyes fade out at a faster rate than the other primary colors, the mixture of the colors becomes primarily red and blue. As this occurs, the film begins looking more purple as you would expect from a mixture of primarily red and blue dyes.

It is important to note that all dyed window films will fade over time. While I realize that some films are warranted against color change and fading, there is simply no way to completely stop the fading process in a dyed film.