There has been a lot of discussion here regarding thermal insulating paints and additives. And much of it somewhat contentious for whatever reason. My personal experience with Hy-tech has indicated a substantial reduction in transmitted radiant heat when the surface is properly treated. They make one product called BusKote which is a rubberized paint that contains ceramic microspheres and they also sell the microspheres separately for use with any type paint.
I have seen and felt it in action on 100+ Houston days and I am using it extensively on my shorty, including a coating on the roof.
Feel free to express whatever, but as noted, having seen what it can do in person, I am going to continue it's use.
My dos centavos.