We all know what it’s like getting into a car that has been parked in the sun. Even with the air-con on at full blast, it takes a while before things cool down.

The use of solar film in cars to keep heat out has been around for some time. Solar film was initially used for buildings and architectural applications before being adapted to vehicles.

To know how window film works, you need some basic understanding of solar energy. As the Earth is directly in the path of solar radiation, we receive heat and light in various wavelengths, some visible and others invisible to the eye. Sunlight is visible light while ultraviolet, infra-red, microwaves, gamma and x-rays cannot be seen.

Approximately 50 per cent of the heat we feel is attributed to visible light while the rest is infra-red radiation falling under the invisible part of the spectrum.

Back in the 1970s, window film was mostly dark-tinted film coloured with dyes. As solar control film, these early versions were not very effective as they only blocked out visible light; heat from infra-red rays could still get in.

Advances in metal deposition technologies led to the next generation of solar film in the 1980s. These highly reflective films proved effective in cutting out heat from both visible and invisible light rays, but they also blocked out visible light and left the car in darkness.

A breakthrough in surface particle science in the late 1980s allowed atom-sized metals to be deposited onto clear film without being reflective. The ability of these new films to allow a high percentage of light to be transmitted made it suitable for use in cars.

This development was called “spectral-selectivity” by its innovator, Southwall Technologies, and it led to the spectrally-selective coatings used in the high performance window film available today.

“Smart” solar film using spectral-selectivity technology, like the kind by V-Kool, can differentiate between wavelengths in the solar spectrum. Heat is reflected, instead of absorbed, by the clear substrate with seven atomic layers of gold, silver and indium oxide, while allowing light to enter.