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How Does Window Film Work

Gauri Huddar
Window films have been around since the 1960s, but since then they have undergone many improvements to suit the needs of the modern home. Let's find out in this story how they work.
What is window film? It is a layer of transparent material, which is applied to windows to block out the harmful radiations that pass through glass, and also to reflect some of the light entering your home/ office/ car. These films are really useful in case the glass area of your house and office is really big. If it is not feasible for you to keep the blinds drawn or the curtains pulled all day, then window films provide an easy alternative. They reduce the glare but do not block out all the sunlight, so you have light while still being protected from harmful radiations. Here is how it works...

How does Window Film Work?

Window films are made of clear polyester. On this clear polyester film, another thin and even film is applied, which is made from various tinting agents, by metal or dye deposition methods. This second film, made from tinting agents/ metals/ dyes, is useful in blocking out the harmful rays that cause fading of colors, the UV-A and UV-B rays which are harmful for the skin and have also increase the risk of cancer when skin is exposed to them.
Although there are different types of window films, all of them work on the following basic principles:
  • Reflection
  • Radiation
  • Absorption
  • Transmittance
The way these work are as follows:
  • The tint reflects a significant portion of the harmful visible and ultraviolet rays, with something called 'sputter coating' (a coating of metal particles), which affects the amount of light that is rejected by the tint. More the amount of sputter coating, more is the rejection.
  • Radiation works well, especially in the winters when the heat in the room is radiated back into it, to avoid it from escaping. This helps keep the room comfortably warm during winter.
  • When sunlight is incident on the window, the tint absorbs a percentage of the UV radiations, and prevents them from being transmitted into the room. Some portion of the visible light is also absorbed by the tint, to reduce the glare in the room/ car.
  • While the tint does absorb and reflect a percentage of the sunlight, it transmits most of the sunlight into the room after filtering it. This helps in case you want to reduce the glare, but not by pulling the curtains or drawing the blinds because that makes the room really dark.
These window tints usually reflect around 5% of visible light (known as VLR%), absorb around 5% of it (known as VLA%) and transmit the remaining 90% visible light into the room (known as VLT%). These percentages may vary, depending on the composition of the film you buy, the manufacturer, the way it is installed, and its quality.
Where and How to Apply the Film?
  • Window film is usually applied on the inside of the glass, to prevent it from getting scratched and damaged, although these days it is standard practice to manufacture films with scratch resistant coating.
  • The films can be applied on normal glass, but if it is applied on plexiglass, it will damage the window when you try to remove the film from the glass. This is because the adhesive that is used to attach the film to the glass, reacts with the plexiglass, and forms a permanent bond.
  • The film should also not be applied on tinted glass. This is mainly because, tinted glass absorbs heat and window films also absorb some heat. If this combination gets too high, then the glass may crack due to excessive thermal stress.
  • Also, window films should not be applied on glass that has stickers, or any other raised irregularities, on its surface. This makes the film stick poorly to the glass surface. 
Make sure that you remove any such things taped to your windows, before applying the film. This will make it easier to clean and maintain it, and you will not have to worry about water or air being introduced between the film and the glass.
  • Window films, on an average, last for anytime between 8 to 12 years. It depends, to some extent, on how you take care of the film and maintain it, besides depending mainly on the quality of the film. Proper care and maintenance will make it last longer.

    Covering your windows is a smart option, since it also prevents the breakage of glass. When glass breaks, the shards usually fly and there is danger of these flying shards injuring people seriously.
    Window film does not tear so easily, so even if the glass breaks, the shards won't fly. This is just one more advantage of using it. Investing in a good quality window film would be a smart choice, be it for your car, office or home.