for heat prevention tint, go for those branded film such as Air Cool, Rike Cool, V-Kool, EcoTint, SafeTint, Milo Tint (just kidding
), etc...It really makes a difference compare with those normal films, trust me..I am using one of the mentioned films, not to say 100% heat resistance, but the car is at least 50% less hotter than it used to be and takes lesser time to cool off in the afternoon when I gets in to the car and turn on the aircond.