It's a dry bag that doubles as a stuff sack. Or a stuff sack that doubles as a dry bag. Take your pick- it does both flawlessly! I have four, in two sizes, and use them in my kayaks as well as in my backpack. They can be compressed into any shape to fit odd-shaped crevices in kayak hatches or gaps in a pack. There's even a hang loop so you can suspend one from a line between two trees to keep your food away from most rodents. GREAT! BUY THEM!!