How Window Film Works
Window film is made out of an optically clear polyester with a very thin layer of tinting agents such as dyes and/or metals deposited onto the film. These layers are assembled and finished with a strong scratch-resistant coating. Window film is always applied to the inner surface of the glass which protects the film from the elements and flying debris outside the car. When applied to the inside surface of glass, window film provides significant solar insulation.
Window tint is available in many different shades to suit your preferences. It is a myth that window film has to be dark to be effective. Unlike sunglasses that do impair your ability to drive at night, window film is designed to reduce glare and not impede night-time driving.
Once tinting film is applied to a window, the characteristics of how visible light comes into the car changes. Normal auto glass without tint reflects around 5% of visible light (known as VLR%), absorbs another 5% (known as VLA%), and transmits 90% of visible light (known as VLT%) into the car.
Depending on the type and quality of tinting film applied to a window, these percentages change dramatically. Some films are more reflective, and others absorb more light. The number you will most commonly see is the VLT% (Visible Light Transmittance). Almost all the official names of films include the VLT% within it like HP Quantum 28.. VLT% tells you how much visible light is allowed to shine into the car, and also indirectly how dark the tint looks.
Tinting film doesn't just block visible light. It also blocks harmful cancer-causing ultra-violet (UV-A and UV-B) rays as well as infra-red (IR) rays that cause heat to build up in your car; however, how effective a film is in blocking these rays depends on the type of film, the manufacturer, and the quality of installation.