7. Contribution of leaks or perforations

Permeation studies can be carried out easily, but leaks complicate the system, as they are uneven, unpredictable and vary from package to package. The perennial question of the "size of the hole" is debated by manufacturers of food, pharmaceutical and medical products. Each has its own criteria.

However, we can agree that, in order to control gas transfer, it should only take place through the packaging material, and not through its defects, unless the latter are controlled and voluntary (as in the case of fruit and vegetables, and intentional perforations). This is an obvious assertion, but its weight can be gauged by observing the size of the defect at which we speak of a gas "leak" (figure 19 , small molecules