u mean mazda give u free skytint and you want to apply another same skytint outside to the front windscreen? What's the benefit of that?
Based on that i had tested from the skytint that was recently removed from my cx5.
the IRR is around 90+
the UV is around 50+
the VLT is around 70+
and its a safety film 6mil if not mistaken
I strongly do not recommend double tint with the reasons below:
1) In most of the cases, it will void both warranty.. the original tint and the new tint that was applied on top of original tint. You may check with the shop.
2) the risk of mistake during application. says u are going to double tint 4 side windows. if during application one of the window tint having prob and when they remove it the original tint was damage along the way.. now u left with 1 windows with single tint another 3 with double tint, are you ok with it?
3) Distortion.. when light pass thru the two tint that might make out of different material, the light may disperse or diffract. It may cause disturbance while you are driving.
Me personally will not recommend but i know a lot of ppl doing it. Even the tint shop i visited they apply double tint to make their car windows darker. So at the end is still your choice to make

No, i only plan changing the front windscreen skytint. Rest of windows will remain as skytint. U are right. I will likely just replace the front windscreen tint with another better brand instead of applying another layer.