Factory tint, commonly referred to as "Privacy Glass" is an electrical process called "deep dipping" that involves dying the inside of automotive glass with a dark pigment. Factory tint is standard on the rear half of many new vehicles. With a common visual light transmission (VLT) of 15%-26%, factory window tint is installed to provide passengers and personal items privacy from outsiders, hence the name privacy glass. Since most states have a VLT legal limit of around 50% for the front driver windows and windshield, factory tint is only applied to the rear half of vehicles windows to avoid breaking the law.
With a low VLT, the primary benefit of factory tint is to provide privacy for passengers and personal items. Unlike window film, factory tint, depending on the car manufacturer and year, does not provide the same ultraviolet (UV) protection or heat reduction qualities. Window film offers 99% UV protection against both UVA and UVB rays. Factory tint provides protection against UVB rays because UVB rays cannot penetrate any kind of glass including non tinted glass.
Unlike window film, factory tint is a pigment within the glass that's installed during the manufacturing process. There is no way to remove the tint from the glass. The only alternative to getting the same benefits of window film is to install window film over the factory tint. There are clear window films for automotive use that won't further darken the factory tint. Many consumers attempt to match the factory tint to their front windows and windshield when it is legal to do so in their local jurisdiction.