Heat Reduction
One major reason people want to have film on their car windows is to reduce HEAT.
Sometimes there can be confusion due to the performance figures (and how they vary) thrown about by different companies.
To find out how 3M can provide true percentage of Heat Reduction take a look below at this simple diagram -
(A) A large proportion is reflected (rejected) out from the glass. This occurs regardless of the surface, e.g. brick and wood still reject heat.
(B) An amount is absorbed by the glass (this make the glass feel hot to touch).
(C) The remaining heat comes through the glass and into the car.
Instead of quoting on figure (C) - which is the heat coming through the glass into the car - most companies include rejected heat (A) and absorbed heat (B) to increase the total percentage of heat rejection off the glass.
This can be misleading as figures (A) and (B) do not contribute to the heat felt by the occupant of the vehicle. Figures A & B should not be included in any heat reduction figures quoted but often are to make heat reduction look more impressive.
3M only consider figure (C) to give a true heat reduction percentage as felt from inside the vehicle.
In addition - USA guidelines were introduced to overcome the confusion and a figure called the "Shading Co-efficient" rating was introduced.
This "Shading Co-efficient" is a mathematical equation that takes in all the film and glass variances and produces a figure. The lower the "Shading Co-efficient" number the better the performance.
