This chapter is a state of the art report focusing on the aspects that concern cool
materials for buildings that are white or light colored. It is structured in four sections; in the
first section cool white or light colored materials i.e. materials characterized by high solar
reflectance and high infrared emittance are defined. Typical values of the two properties are
given according to independent studies, the U.S. Cool Roof Rating Council‘s database and
the IEE Cool Roofs project database. The impact of solar reflectance and infrared
emittance on the surface temperature is explained and performance examples according to
experimental results are compiled. The second section focuses on the types of cool white
colored materials that are commercially available per roof type. These include build up
roofs, single ply membranes, modified bitumen, tiles, coatings, metal roofs etc. A short
description of each technology is given and their main characteristics are reported. The
benefits of using cool white colored materials on buildings and the urban environment are
analyzed in the third section. The benefits include increased thermal comfort conditions in
buildings, reduced cooling energy consumption and peak electricity loads, increased life
span of the roof system, reduction of the air pollution and greenhouse gas emissions and
mitigation of the heat island effect. Each one of these benefits will be supported by
experimental and simulation data available in the bibliography. Finally, the problem of
ageing is analyzed. Exposure of cool materials to outdoor conditions has the effect of
changing their main properties: solar reflectance and infrared emittance, compromising
their performance. The main mechanisms (photo-degradation, thermal stress, deposition of
pollutants etc.) that are responsible for causing the ageing effect of the materials are
reported. Experimental results that estimate the aging effect of various types of materials
and for several outdoor conditions are presented. The case of artificial and natural ageing is
discussed as well as any effort to model the ageing effect of cool materials.
Keywords: White cool materials, cool roofs, optical properties.
