For the Multiangle Imaging SpectroRadiometer (MISR), currently under development for the Earth Observing System, we plan to use deployable diffuse reflectance panels to provide a flight calibration of its nine cameras. Near-lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons and to allow each camera to be calibrated under the same illumination levels. Panel spatial and spectral uniformity and stability with time are also required. Spectralon™, a commercially available diffuse reflectance material made from polytetrafluoroethylene (PTFE), has been baselined in the MISR design. To assess the suitability ofthis material, a series of environmental exposure tests were performed. No degradation of the optical properties was apparent following proton bombardment, and stability through UV illumination was satisfactory, provided simple cleaning and handling procedures were implemented. One surprise during the testing, however, was a buildup of several thousand volts of static charge, which developed while simulating a rare pass through an auroral storm. Such a potential for charge buildup is not unique to PTFE, but exists for many thermal control paints used to cover spacecraft exteriors. Further testing of the charged Spectralon failed to produce arcing to the metallic housing frame, and models indicate that charge neutralization will occur after passage through the storm. For these reasons we intend to fly Spectralon as per our original plan.