Sealock is a dry bag manufacturer and OEM supplier. Ask around the paddling world and you'll get two confident and apparently contradictory answers: that a roll-top is the most reliable seal there is, and that only a proper waterproof zipper is genuinely submersible. Both are right, because they're measuring different things — one is talking about failure rate in the field, the other about sealing performance under sustained pressure. Our standard dry bag range is built around the roll-top, which is the right closure for the great majority of dry bag use; a waterproof zipper is available as a custom closure where a project genuinely calls for it. This guide separates the two so a brand can specify the closure its customers actually need.