What are reflectivity and solar reflectance?
Reflectivity is a measure of the solar reflectance of a surface. Reflectivity is defined as the ratio of the reflected solar radiation flux to the incident flux. Reflectivity values range between 0 and 1 with the higher number indicating higher reflectivity. This is also sometimes expressed as a percentage from 0% to 100%. A more reflective roof will reflect the solar radiation away from the surface rather than absorbing it. Absorbed solar radiation will increase the surface temperature. There are standardized methods to measure the solar reflectance of roofing materials like ASTM E903 and ASTM E1918.
