Yes, F-stop bags are indeed waterproof. They use a combination of materials and technologies to keep the contents inside dry, even in heavy rain or submersion. Their main material is ripstop nylon with a TPU coating which creates an airtight seal on the seams of their packs. Additionally, they have welded zippers that further enhance water resistance as well as a rolltop closure system for added security against wet conditions. Lastly, F-stop also tests each bag before it leaves their facility to ensure its waterproofing capabilities meet their high standards.