Efficient packing and a no-H2O zone. These tough bags have a purge valve to vent air and keep them compact. The rectangular shape creates less dead air space inside your pack, kayak or cycle touring panniers. Made from lightweight yet durable 70-denier polyurethane-coated nylon. Fully radio frequency welded seams create a stronger and more durably waterproof construction than sewn and taped seams. One-way PurgeAir valve vents trapped air while remaining waterproof so you can compress the bag. Internal roll top closure is easy to use and seals tight. 4-strap Continuous Compression system encircles the bag to minimize seam strain while still letting you compress your load. PackTight shape features flat-side rectangular shapes that nestle close to together so there's less wasted space.