The goal of packaging is to provide a consistent barrier between a product and the surrounding environment. 

Permeation is defined as the movement of molecules from one side of a barrier to the other. This process follows a solution-diffusion mechanism where gas absorbs at the package wall (polymer), diffuses through the polymer, and desorbs/outgases on the other side. 

Permeation testing is necessary to ensure that a product's packaging will provide the desired shelf life. To learn more about the factors that influence permeation, see the article in the Related Resources column.