The reflector has a bilayer structure with a -thick depth-graded multilayer, a -thick epoxy, and a -thick aluminum substrate. Wrinkle formation in such bilayers resulting from compressive stresses due to a heat load is a well-known problem (e.g., 3). The wrinkles also degrade the performance of the x-ray reflection so that it is critical to know the upper and lower temperature boundaries for which the wrinkles do not form. We, therefore, performed thermal stress tests of the depth-graded Pt/C reflectors used by the ASTRO-H HXT. Such replicated thin-foil reflectors are planned for many future missions.4–9 A record of the storage temperature is, therefore, useful in order to quickly examine the validity of a given thermal environment of such satellite systems.