Movement of gas or vapour through a solid barrier material.
Also called: gas permeation; water vapour permeation; water vapor permeation.
Can an intact plastic barrier still transmit moisture?
Yes. Permeation involves uptake at one surface, diffusion through the material and release at the other. It differs from flow through a discrete hole or seal channel. Water-vapour testing can use a barrier specimen between controlled wet and dry environments.
For packaging selection, the useful distinction is the transfer mechanism. A low-leak result does not establish zero oxygen or water-vapor transmission through intact polymer. Conversely, a film transmission result does not demonstrate that the formed and sealed package has no defects.
Check the permeant, temperature, humidity or gas-pressure difference, exposed area, material structure and thickness. Conditions on both sides of the specimen matter. Results under different boundaries are not interchangeable measurements of an unconditional material property.
Transmission rate, permeability coefficient and total package transfer describe different quantities. State the construction and geometry for coated films, multilayers and formed cavities, then use the reporting basis appropriate to that specimen.