If I were to do my window personally, I would use a 70% or 80% film, BUT it is not considered legal. It would be really really, really hard to know if that someone had an 80% film on their car. I am kind of a black-and-white person, though. Let's say a little kid jumps in front of my car, and it would not normally be my fault.... Does a lawyer get ahold of that and try and turn it from a traffic infraction to a crime... I have no idea, but it is worth thinking about. Same with going darker than your state allows
