COLD MATERIALS

Cold materials are those that are characterized by two basic behaviours:

1. High reflectance to solar radiation (total solar reflectance). Reflectance is the ability of a surface to deflect (reflect) incident solar radiation It also includes radiation in the visible spectrum and the infrared and ultraviolet radiation which are included in solar radiation spectrum.
2. High infrared emittance. The emissivity is a parameter that determines the ability of a material to dissipate amounts of heat in the form of infrared radiation.

The above characteristics are expressed in values ranging from 0 to 1 (0% - 100%). The higher the value is, the "cooler" the surface, i.e. the lower the surface temperature developed on it. Therefore: 100% = total reflection, 0% = zero reflection (i.e. 100% absorption).

The solar reflectance index (SRI) incorporates both of these properties into one value, by determining the ability of a surface to reflect solar radiation and to emit, in the form of infrared radiation, the energy which has absorbed. It is a function of the increase in its temperature compared to a standard white and black surface. Essentially, the SRI coefficient characterizes how 'cold' a material is.