Early window films were little more than coloured polyester, called dyed films and they provided only limited UV, heat and glare protection. Some window films are still dyed to give them a nice dark look, but they gradually fade, depending on the amount of sunlight they are exposed to.
The breakthrough in window film design came in the form of metalized coatings. Metal, usually aluminium, is super heated in an electric furnace to form a vapour and the vapour is passed over the polyester film. A very thin layer of metal is “deposited” onto the polyester film. This thin metal coating serves to reflect heat and tint the film.
The next step in the evolution of window tinting film happened when NASA decided to send man into space. Window films made using the aluminium deposition process were not up to the extreme conditions of space and NASA was forced to find a better way to protect the astronauts from the heat of the sun.
NASA turned to a metal coating process called “sputtering”. Silver is one of the best heat “reflectors” and can be deposited onto a polyester film by sputtering. Multiple layers of silver, nickel, other metals and non-metal ceramics and carbon can also be deposited on the polyester film. This means that different materials can be selected for their unique spectral properties and allow truly “smart” films to be made. Films that will block certain wavelengths in the spectrum while letting other wavelengths to pass through. That’s how these films can block heat while letting in enough visible light to not darken rooms too much.
Most window films are self adhesive with a backing sheet that is removed immediately before applying to the glass. Soapy water is sprayed onto the glass and film to allow air bubbles to be squeegeed out. The water then soaks into the glue activating the adhesive, and slowly dries to form a strong bond with the glass.