) is the ratio of the radiant emittance of heat of a specific object or surface to that of a standard black body.
[1][2] For building products, thermal emittance measurements are taken for wavelengths in the infrared.
A roofing surface with high solar reflectance and high thermal emittance will reflect solar heat and release absorbed heat readily.
In common construction applications, the thermal emittance of a surface is usually higher than 0.8–0.85.
[1] High thermal emittance materials are essential to passive daytime radiative cooling, which uses surfaces high in thermal emittance and solar reflectance to lower surface temperatures by dissipating heat to outer space.