Multilayer process: the addition of the plastic film was the first step to create brick containers impermeable to liquids and warmth-sealable. During the sixties, an aluminum foil started to be additional towards the cardboard container to make sure much better security and increase the shelf life of the packaged item. https://medium.com/@GabletopPak/innovative-packaging-solutions-for-dairy-products-brand-identity-with-gable-top-cartons-d9ed6dad17c5