Space instruments such as solar arrays, radiators, or optics can be strongly impacted by molecular contaminants outgassed from spacecraft materials. For optics, transmittance and reflectance performances could indeed be modified by the deposit of contaminants. We report the transmittance measurements and predictions in the ultraviolet–visible–near-infrared range of contaminated optics from the outgassing of a mixture of two common materials used in space industry: EC2216 material (epoxy compound) and RTVS691 material (silicone compound). The Swanepoel model, commonly used in many fields, was employed for the first time in such conditions to easily and quickly predict transmittance. Transmittance was fully recovered at 20°C; a decontamination plan could be based on heating at this temperature at least during a duration depending on the silicone/epoxy contaminants layer thickness.