How Heat Reflective Paint Works

How does Heat Reflective Paint work? There are two major factors that make a heat reflective paint successful - Emissivity and Solar Reflectance. 

How is a successful heat reflective paint measured? Both emissivity and reflectance is measured in one combined value, name Solar Reflectance Index (SRI).

This is the superior measure as it combines both of the most important factors. If the paint you're considering doesn't advise it's SRI, it would pay to determine it.