We have measured the permeation rates of helium and water through thin-foil UV-blocking filters used in the ASTRO-E/X-Ray Spectrometer (XRS) instrument. In the XRS program, there is a concern that outgassed contaminants such as water couldpermeate through the outermost filter, which will be at room temperature, and freeze on the inner filters, which will be at cryogenic temperatures. The filters tested consisted of ~1000 A Al on ~1000 A of either Lexan or polyimide. Results discussedinclude the permeation rate as a function of pressure difference across a filter, the ratio of helium to water permeation rate, and the effect of the aluminum layer thickness on permeation.
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