I’ve never really worried about how small I can compress a down bag. (A 25 degree bag with 800-fill power will, I think, compress to about the size of a softball or one-liter bottle?) However, if I use a compressor sack to get to that size, I’m left with a very stiff, unyielding item that can be difficult to pack around. As a result, I’m left with little empty spaces and an overall load that isn’t any more compact. (Those empty spaces undo all the space saving of compressing the bag - and compression probably doesn’t do the down fill any good.)

I tend to put my sleeping bag in the bottom of the bag, uncompressed. As I add gear, it compresses the bag more naturally, filling all the voids, and I can shift the shape as needed to accommodate long or bulky items. Until recently, I didn’t use a stuff sack (but was very careful about not setting my pack in puddles or mud.) Recently, I’ve begun using a 40 liter stuff sack that doubles as a pump sack for my sleeping mat. This works about the same as putting the bag in loose.