It has the same waterproof protection trusted by SeaLine® Dry Sacks, but the BlockerTM PurgeAirTM also features a built-in waterproof valve that fully purges trapped air. That means no more ballooning—and no more wasting precious packing space. Plus, flat-sided PackTightTM shape means multiple Sacks can nestle closely together for 20% more packing efficiency than rounded sacks. Lightweight 70D polyurethane-coated nylon is a tougher, more resilient cousin to the ultralight BlockerLite materials. More durable and versatile, and great for all-around use with confident waterproof protection.