Polyethylene Coating: A thin layer of polyethylene on each side offers durability. The outer layer shields the design and printing, whilst the inner layer functions as being a sealant, producing the carton wholly leakproof. The main patents for foodstuff paperboard containers date back to the beginning of the last century. https://www.tumblr.com/sustainablemilkcartons/780351921897816064/how-gable-top-packaging-is-shaping-the-future-of?source=share