Windshield Heat Rejection Film: What the Numbers Actually Mean
Sun film is sold on three numbers and only one of them describes how cool the car will actually be. The other two are what gets quoted at you.
The three numbers
VLT — visible light transmission
How dark the film looks, as a percentage of light let through. This is the number the law regulates, and it says nothing about heat.
IR rejection
Measured at a single wavelength, which is why it is the number cheap film advertises. A film can claim a very high IR figure and still pass plenty of heat.
TSER — total solar energy rejected
**This is the one that matters.** It accounts for visible light, infrared and ultraviolet together — which is what your cabin actually experiences parked on MG Road in April.
Dark does not mean cool
A good windshield film can be almost clear and still reject a large share of solar energy. That is the point: you are not trying to make the glass dark, you are trying to stop the dashboard becoming too hot to touch.
Darkness and heat rejection are separate properties, whatever the roadside shop tells you.
Bring the car in and we will show you the spec sheet for the exact film before anything is fitted.
What to ask for
- The manufacturer's spec sheet for the **exact film**, not the product range
- The TSER figure, not just IR rejection
- Your state's VLT limit for the windshield, checked before you commit
- The warranty card, issued at handover
A film that is legal on side glass may not be legal at the front, so confirm the windshield limit separately. Our [sun control film and glass coating](/services/glass-sun-control-film-bangalore) page lists what we fit.
Film and coating are different jobs
Sun film manages heat. A [windshield glass coating](/service/windshield-glass-coating-new) makes rain bead and clear at speed, which mostly helps night driving in the monsoon. People ask about them together, but they solve unrelated problems and are priced separately.