Since materials of plastomer materials of synthetic resin have a large outgassing rate than metals, they are not so suitable for use as uhv components. However, some of the plastomers are often installed in vacuum system, where their low electrical- and thermal-conductivity are required. The outgassing rates were measured for bulk samples of FRP, PEEK and polyimide, and for thin sheets of PET (Aluminum deposited PET film of 9 μm thick.) and polyimide. The outgassing rate is decreased in a manner of t^−1/2, indicating diffusion process of absorbed gas molecules from bulk. The rate of sheet, being after several tens hour pumping, shows rapid decrease. The effect of bake-out degassing in vacuum is also examined for bulk plastomers.