In space research electrostatic analyzers are frequently used in combination with time-of-flight spectrometers and/or secondary-electron multipliers. The purpose of such electrostatic analyzers is not only to determine the energy-to-charge ratios of particles but also to separate charged particles from EUV light. Since most particle detectors are extremely sensitive to EUV, substantial suppression factors are required in order to limit the undesired background counts caused by EUV radiation. For instance, in a typical application for the investigation of the solar-wind ion composition, a number ratio of EUV photons to minor ions of the order of i09 is encountered. Hence, the quality of an energy analyzer system crucially depends on the optical design and on the EUV reflection properties of the materials used. We present results from an investigation of EUV reflection properties of several materials that are frequently employed for the construction or for the surface treatment of ion-optical instruments in space research.