I have the 25L in this bag. I fit a full sleeping bag a 3 person tent and a change of clothes in this no problem. A dry sack with the ability to be compressed is priceless in backpacking. I am on the lookout to buy a few more smaller sizes of these. Great for canoeing!
This is a built to last, heavy duty dry compression sack. As good as, if not better than, the Sea to Summit equivalent. I would also check out OR Drycomp summit sacks, it makes for a great summit pack.