The new Sea to Summit Ultra-Sil Dry Sacks are more than 50% lighter than our super popular Dry Sacks. Theyre made of Siliconized Cordura, which is one of the lightest and toughest waterproof nylon fabrics available. Now you dont have to choose between keeping your gear dry and keeping it light. Proper Use: Any roll-top dry sack must be closed properly to ensure water cant get in. Begin by folding the Hypalon strip down first and be sure to have at least three rolls before closing the buckle. Avoid contact with sharp objects or subjecting the sack to high abrasion, as this could compromise the waterproof fabric. Like all manufacturers of roll-top, fabric dry sacks, Sea to Summit recommends that sensitive electronic devices be double bagged (i.e. putting electronics inside one dry sack then placing this inside a second dry sack). For maximum protection, the use of a waterproof hard case should be considered.