I can't seem to fit my sleeping bag in the designated compartment. I even got a compression sack and it's still not small enough to fit there... maybe I need to get a more lightweight sleeping bag that can compact more. Other than that, this bag is pretty great. Lots of little features that are going to be very handy while hiking. I got their 3L Hydraulics Reservoir along with this and it fits pretty well. It is hard to take the pack out for refilling without the bag being empty, so now I see why their more expensive versions have the hydration pack compartment on the outside of the bag.