Installers use infrared meters, but there is a simple check you can do at home once the film has cured. Lower a window part way in the sun so half the pane is tinted and half is clear, then feel the difference in warmth on each side with your hand. It is a rough comparison rather than a measurement, but it gives you a feel for what the film is doing. For real numbers, ask for the data sheet on the film fitted to your car.
Wheeling TESLA window tint Highlights: – Independent installers – Reduced view into the cabin – Solar heat management