Depending on its “chemistry,” the permeable material can be quite selective allowing some fluids to pass while other are almost completely blocked. A common example being hydrophobic membranes like PTFE blocking liquid water, but passing air and water vapor.
Permeation measurements can be an advantage when used in many polymer and paper manufacturing applications where penetrating fluids might alter the properties (durability, odor, taste) of the product. Since different materials have different permeation abilities, knowing the permeability rate is often crucial for developing new products. Parameters influencing permeation are the penetrating fluid, applied pressure, temperature, material thickness and surface area.
Permeation is measured in SI units of mol/(m s Pa).
The permeation of films and membranes can be determined by observing the fluids of interest passing through the specific material during a relevant amount of time. This method has however some drawbacks, as it is time-consuming and sometimes complicated.