A procedure is described for evaluating the solar reflectance of building materials by using a spectrophotometer. The point is that one should use the calibrated diffuser as a standard reference for reflectance; values of sample reflectance measured with a calibrated polytetrafluoroethylene resin (PTFE) are most reliable. Pressed barium sulfate, which is widely used in colorimetry, is not adequate as a standard reference for measuring the solar reflectance.
