Scorching heat inside the car

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In some countries, and for good reason, it is illegal to put tints that are darker than 70% and/or having a VLT lower than 90% below the AS1 line. This line is typically 4-5 inches from the upper edge of the front windshield. Though, it can vary slightly from vehicle to vehicle. You can put a strip of tint of any shade above this line, but only tints specified above are typically allowed below the line.



There's an optical difference above and below this line. The quality of the optics below this line has better clarity than the part of glass above the line. In contrast, side windows including the rear windshield is only rated AS2 (some are even AS3) which are typically of lower clarity. Hence the importance of the front windshield's AS1 area as this is what any driver use to operate the vehicle 99% of the time.

More info on windshield markings here: Car Windshield Markings: names, sample images, meaning