Once a BFS container or a card of containers has been inspected for quality and prepared for packaging, it is usually wrapped in a hermetically-sealed foil pouch.
Foil as secondary packaging serves two major functions to help protect the drug product during storage.
The first is to slow the gas permeation across the pharmaceutical-grade plastic. Foil overwrapping is commonly performed with an inert gas overlay, such as nitrogen, to prevent oxidation of the drug product from occurring.
The second reason for foil overwrapping is to prevent moisture transmission across the pharmaceutical-grade plastic container during extended storage.