There are three major ways to achieve tinted windows:
OEM tinted glass is tinted within the glass, as part of the actual glassmaking process. It lasts the life of the glass. OEM tinted glass usually has only a mild tint that is legal even in the most stringent areas. Keep in mind that OEM tinted glass may be more expensive to replace in a collision.
Film tinting is by far the most popular aftermarket method. A thin tinted polymer film is applied very carefully to specially prepared window glass. The film is available in many different shades of tint and outward appearances, such as flat, reflective, metallic, or even mirrored. Advantages of film tinting are that it’s very inexpensive, and installers claim that it also might help prevent glass from shattering in crashes. Disadvantages are that the film tinting will only typically last five years before cracking, peeling, and bubbling of the plastic film occurs, and also sometimes yellowing or degradation of the tinting itself. Removal of old window film is more difficult than the installation itself.
If you have a shop do the work, make sure they’re approved through an industry group such as the International Window Film Association (IWFA). Also, check that they always use the same brand of film (3M and Johnson are two of the major brands), and that they fully support the manufacturer’s warranty.
You might be tempted by tinted window films — the type available at discount auto parts stores and department stores — claiming easy “stick-on” installation and only requiring scissors or a razor blade for installation. Beware that these solutions sometimes end up with bubbles or wrinkles and rarely end up looking professional, and again, removal is usually more difficult than installation.
Coating tinting applies a special tinted solution to the existing glass, usually as a spray. This type of tint lasts much longer than film tinting, though there are few shops who do it for automotive glass because if properly done it requires removal of the window glass.