This Large Compression Stuff Sack was designed for the 5-part Improved Modular Sleep System, but it can be used to compress most sleeping bags or even clothing. It's constructed with water resistant material with adequate volume for both bags and the bivy cover too. Take the excess air out of everything that fits in this sack and you'll be amazed at how much space you gain. Perfect for organizing a bug out bag or storing off season clothes. Make the most out of your limited space.