Even though the job basically looks done once the headlights are polished and sanded, the plastic still needs to be protected from UV light so it doesn’t just get cloudy again. UV rays cause the plastics in most cars’ headlight covers to oxidize, turning the clear polymers cloudy and yellow. It’s more or less similar to what goes on when you cook egg whites, just with plastic instead of protein. Different kits on the market differ in their solutions to this. Some such as the Sylvania kit, our best headlight restoration kit top pick, include a durable clear film that’s guaranteed to ward off corrosion for the lifetime of the car (or the headlight assembly.) Others typically offer a spray coating that lasts around a year, depending on whether you keep it garaged and what the climate is like. Environmental factors mostly determine how long these headlight restorations stay looking new. Intense sunlight will corrode the plastics faster, for instance, while salty air, road salt in winter or desert sandstorms wear away clear UV coatings faster.