Outgassing is gas release from materials or their surfaces into the surrounding space. In a vacuum chamber it contributes to the gas load, even when the seals have no leak. Adsorbed water and dissolved gases can have very different release times.
The relation shows why surface preparation and material choice matter: increasing pumping speed addresses removal, while reducing outgassing addresses the source. A pressure-rise measurement with pumping isolated estimates total release only after accounting for leaks and temperature changes.[ref]
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Outgassing refers to the release of gas that was dissolved, trapped, frozen, or absorbed in some material. This phenomenon is particularly significant in various scientific fields, including materials science, environmental science, and space exploration. In the context of materials, outgassing can occur when certain materials, such as plastics, metals, or composites, are heated or placed under vacuum conditions.