Permeation
From ExoDictionary
Permeation
As applied to gas flow through solids, the passage of gas into, through, and out of a solid barrier having no holes large enough to permit more than a small fraction of the gas to pass through any one hole. The process always involves diffusion through the solid and may involve various surface phenomena, such as sorption, dissociation, migration, and desorption of the gas molecules.
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
