I think I have the 20 L stuff sack (with the Event on just one end for air to escape) for my 20deg extra wide down quilt and my full length thermarest Xtherm, and there is plenty of room. I am lazy (aka efficient for some), so I just roll the quilt and air mattress both up together and place in the stuff sack. But as said above, it is much nicer having the bigger stuff sack to start off with to get everything in, and then roll the top of the sack down slowly compressing everything into about 1/3 of the original starting volume.