Generally speaking, it is a urethane film with an adhesive backing that is applied to painted surfaces of vehicles to protect their paint from rocks, salt, insects and other driving debris. Some companies have proprietary top coats that make the film hydrophobic (for easier cleaning) and self-healing (for micro-scratches during washing). Most films are 8 mils thick (8 thousandths of an inch) including their top coat and adhesive. It is pliable so as to stretch and conform to the curves of vehicles but does have limitations in complex curves, or curves that extend in multiple directions. It is applied with a wet soapy solution and installers also use a rubbing alcohol solution during installation.
The film is designed to take the impacts instead of your paint. While the film is not impenetrable, the vast majority of impacts will not be noticeable over time. However, larger or sharper impacts can leave a small nick in the film. Be aware that there are companies making very low quality film, usually PVC/Vinyl which is more of a plastic film that may not hold up over time as we have seen personally over the years. Films can be removed if necessary but keep in mind that if it is well past its lifetime then the removal can be costly and time-consuming. It is recommended to regularly wash and wax your vehicle even after the clear bra is installed/
Capital Paint Protection Film in the Raleigh, NC area uses Suntek Ultra with a hydrophobic and self-healing top coat and comes with a 10-year warranty against yellowing, peeling and cracking.