I’ve had a Sea to Summit Ultra-Sil Dry Sack for a few years, and I’ve put it through a fair amount of use. I’ve found it to be a good dry bag for both canoeing and backpacking trips and it hasn’t torn or malfunctioned yet.
The dry bag is made of Cordura nylon, which is waterproof. The inside is also coated in Polyurethane, which increases durability. Lastly, the dry bag features a “Hypalon® watertight roll-top closure” (per REI’s description) that prevents water from leaking in. All you have to do is roll it down at least 3 or 4 times.
Although the Ultra-Sil Dry Sack is okay for canoeing trips, it’s not the best, due to the fact that if submerged, the contents might get wet because it’s not completely waterproof when that exposed to moisture. This is why the dry sack is best for backpacking. I use it either to put my sleeping bag in (and once in my backpack, it pretty much guarantee’s the bags dryness) or to put my clothes in, after which I kneel on it to get all of the air out. This way it acts as a compression bag and protects my clothes at the same time. Pretty good, right?
The price of the Sea to Summit Ultra-Sil Dry Sack is pretty reasonable at REI and it comes in a range of sizes: 2, 4, 8, 13, 20, and 35 liters. I definitely recommend getting it to keep your gear dry!