Polyethylene Coating: A thin layer of polyethylene on either side gives longevity. The outer layer shields the look and printing, when the internal layer acts as being a sealant, making the carton totally leakproof. The 1st patents for food paperboard containers date back to the beginning of the final century. https://medium.com/@GableTopPackaging/where-to-buy-white-label-water-in-paper-pak-77f5dafcee50?postPublishedType=initial