Cool colors for Summer: Characterizing the Radiative Properties of Pigments for Cool Roofs

April 22, 2004 - 12:00pm

In recent years roofing manufacturers have incorporated near-infrared (NIR) reflecting pigments in coatings applied to a variety of nonwhite roofing products, such as metal panels and clay tiles. We have developed and validated a model for computation of solar spectral absorption (K) and backscattering (S) coefficients, and used it to characterize a wide variety of pigments that may be used in architectural coatings.Measured values of backscattering coefficients for generic titanium dioxide (rutile) white pigment are in rough agreement with values computed from Mie theory. Pigments in widespread use are examined, with particular emphasis on those that may be useful for formulating non-white, NIR-reflective materials that stay cool in the sun. High NIR reflectance can be produced by using a strongly NIR-scattering pigment, such as a mixed-metal oxide complex inorganic colorant, or by applying an NIR-transmitting pigmented coating over an NIR-reflective substrate. NIR-absorptive pigments are to be avoidedMore information on the Cool Colors Project can be found at information on EETD's Heat Island Group can be found at

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