Here's what other sites are saying:
Wildwasser Overnighter Storage Float Bags - These dry floats are the most versatile dry storage available. They can be used in the bow and stern compartment of touring boats, or the stern of any whitewater boat. They are built with a 210 Denier PVC base, and super-soft 1500 Denier polyester roll top closure. The valve system on the Overnighters can be used for inflation while used as a float bag, or left deflated in storage mode. Cleats are included so you can tie the bags into your boat, or rig backpack style shoulder straps for portages and small hikes. Flotation is a very important safety essential. Floatation bags limit the amount of water that can enter the boat should a wet exit (after a capsize) be necessary. Self-rescue becomes much easier and less laborious with these safety bags in place. Small is 28.5' x 12.5' unrolled with volume of 1037 cu in. Large is 41' x 14' unrolled with a volume of 1778 cu in.