There are many different window films on the market and some do not perform as well as others. Window film will begin to deteriorate by being exposed to high temperatures (IR rays) and UV rays over an extended period of years. Low quality films fail at a much faster rate.
There are several types of window film failures. These are the most predominate issues:
The yellow colorants in dye based films begin to breakdown turning the film purple or fading out completely. When discoloration begins to occur it accelerates the deterioration of the film (solar rays will attack the molecular structure of the film/plastic).
Happens when a chemical reaction with the adhesive causes oxidation to occur. There are many reasons for this oxidation to occur, from low quality adhesives to sub-standard film application. Window film being exposed for an extended period of time to the sun and its harsh UV rays, heat (IR rays) and visible light can initiate a chemical reaction. High quality films such as Solar Gard films combined with professional installation will minimize this chemical reaction from occurring (hence the reason you get a lifetime warranty with Solar Gard films).
Delamination can occur in long streaks across the middle of the film or start on the edges moving inward. This usually happens in multi-layer poorly manufactured films. Again since window film is applied to a glass pane that receives direct sunlight, the solar energy over time will cause film to breakdown. Using a high end film such as Solar Gard window films, will avoid you from having this issue.
Poor quality adhesive or incorrect film application can cause window film to start peeling. Sometimes this can be repairable but most often it needs replacement.