Most of the factory tint on the clear glass is roughly seventy percent visible light transmission (VLT) and rear factory tint on many trucks and SUVs is roughly at twenty percent VLT. The heat and UV rejections on many factory tints are limited. You can boost the performance of the factory tint without making them noticeably darker by adding a 70% virtually clear or 50% slightly tinted tint on top of the factory tint. On the other hand if you like more privacy, you can choose to add a darker tint. If you add a 35% tint on top of the factory 20% tint for example, it will end up at roughly 7%. The equation is 35 x 20/100 = 7% VLT.
If installing our window film on a flat or very slightly contour glass, it does not require heat shrinking. For example, rear windshield for trucks and many side windows on the SUVs, mini vans, and trucks.
If going on a contour glass, for example not all but many side windows for cars and almost all rear windshield for most types of vehicle except trucks, the film needs to be heat shrunk with a heat gun on the outside glass prior to installing it on the inside.