It's a compression sack with a square cross-section like the Air Bloc Solid, and it's a roll-top drybag with an eVENT bottom like the AirVent HD Reduction DryBloc. That means you can throw your clothing and sleeping bags in it, roll the waterproof top closed and compress it, forcing the air out the eVENT bottom. Not bad.
If you're looking for all those features, say for a Muldrow approach on Denali with the requisite river crossing and other low-altitude wetness, the AirVent DryBloc Solid is a great choice. Available in four sizes.