These rolls are made up of two sheets of brown kraft paper separated by a layer of bitumen to provide strong, effective and reliable water resistant protection. Kraft union paper rolls are ideal for export packaging, crate lining and in other applications where a water vapour resistant barrier is beneficial. Bitumen, also known as asphalt, is either a naturally occuring or refined product. It is also what God tells Noah to use to line the ark before the flood to make it waterproof.