One way to measure how "cool" a roof can be is by calculating its Solar Reflectance Index (SRI). This index is calculated following ASTM Standard E1980-11 using a roof product's solar reflectance and thermal emittance values. The SRI calculation can also be used to estimate the surface temperature of the roof product under prescribed conditions. High SRI values indicate "cooler" roofing products. To calculate SRI, download the SRI Calculator and enter the solar reflectance value (R) and the thermal emittance value (E) as decimals, then click on "Update SRI". Note: macros must be enabled in Excel.