The honest answer is that film performance is measured with proper equipment: installers use an infrared thermometer or a heat lamp demonstration to show the difference between treated and untreated glass. At home, the comparison most owners notice is simply how the cabin feels after the car has sat in full sun, and how much less glare reaches their eyes on a bright drive. If you want the numbers, ask your installer to compare the published specifications for the exact film and shade fitted to your Tesla.
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