Spacecraft components for passive thermal control need to resist degradation in the space environment. The Materials on International Space Station Experiment (MISSE) 11th and 15th flights and the Materials Exposure and Technology Innovation in Space 1st and 2nd flights exposed a variety of materials to the low-Earth-orbital environment. Materials analyzed in this effort include thermal control coatings with ceramic or silicone binders, components for multilayer insulation blankets, and chemical conversion coatings per MIL-DTL-5541. Space environmental and molecular contamination effects on optical properties are reviewed. Future MISSE experiments are discussed.