Multilayer process: the addition of a plastic movie was the initial step to make brick containers impermeable to liquids and heat-sealable. Inside the sixties, an aluminum foil started to be extra to the cardboard container to be certain much better protection and increase the shelf life of the packaged product. https://www.diigo.com/item/note/b5sxz/pq9y?k=67d2da1967c1a3387dbfae19f2467b09