Coating is a moisture barrier applied to the inside of the woven polypropylene fabric. A common type of "coating" is a 1 mil. Thick lamination of heated polypropylene, which is laminated to the inside of the fabric. The lamination provides a moisture barrier to protect the contents of the bag.Since a bulk bag's fabric is made from a woven material, the bag is not "water proof". Lamination is simply a moisture barrier, however the use of an internal poly liner works better in many typical applications, it still is not 100% water proof. Liners and Lamination are designed to keep water away from the product. For more specific requirements, such as oxygen barrier or liquid liners, we suggest a specialized liner. Click here from more info on specialized liners.