Satellite instruments operating in the reflective solar wavelength region often require accurate and precise determination of the Bidirectional Reflectance Distribution Function (BRDF) of laboratory based diffusers used in their pre-flight calibrations. In this paper we present gray Spectralon BRDF measured using a monochromatic broadband source at ultraviolet, visible and near-infrared wavelengths. By comparing these results, we quantitatively examine the wavelength and geometrical scatter properties of gray-scale Spectralon. The Spectralon diffusers with specified hemispherical reflectances of 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 99% were measured using P and S incident polarized light over a range of incident and scatter angles. The measurements are compared, and the influence of material composition on the BRDF is described. The future application of gray-scale Spectralon in the calibration of spaceborne sensors is described. All data were obtained using the out-of-plane scatterometer located in NASA's Goddard Space Flight Center's Diffuser Calibration Facility. The results are NIST traceable.