Gold (uncoated) outperforms all other uncoated metallic reflectors in the infrared wavelength range. Gold’s high reflectivity in the red portion of the visible spectrum is apparent by it’s yellow hue. Because of its ~ 95 % high reflectivity in the 800 nm to 20 µm wavelength range, gold is the best choice for surface coating of integrating spheres used in IR applications. The diffuse reflectivity required for uniform light distribution inside the sphere is achieved through an exact diffuse preparation processing of the hollow spheres interior surface.