Does window film reduce heat?

Solar control film works on the part of sunlight you cannot see. Most of the heat arriving through glass is near-infrared energy, and spectrally selective films are engineered to reject a high proportion of it while letting visible light through. That is why a modern film can leave a space bright but noticeably cooler.

The measure to ask for is total solar energy rejected, which is one minus the solar heat gain coefficient of the filmed glass. It describes the whole assembly, not just the film, so it is the only number worth comparing between options.

For evidence at building scale, the US General Services Administration ran a field evaluation of low-emissivity window film across seven climate zones. It reported an average 29% reduction in annual HVAC energy use within a roughly 15-foot perimeter zone, payback in the range of two to six years, and an installed cost of about $7.75 per square foot at the time of the study.

There is an important caveat. Films that absorb solar energy raise the glass temperature, and not all glass tolerates that. Tempered glass handles a large temperature differential; annealed glass handles far less, and sealed units need specific consideration. That is why we record the glass build during the survey and specify from it, rather than applying a single product everywhere.

What affects the result

• Which film is specified, and its published total solar energy rejected figure
• Orientation and how much direct sun the glazing receives
• How much of the floor area sits in the perimeter zone
• The existing glass: single pane, sealed unit, tinted or already coated
• Whether the glass type can safely carry an absorptive film

Ask us for the performance data on the exact film and glass combination for your building. Generic percentages are marketing; the manufacturer's figures for your assembly are a specification.