I'm with Phat and Howie - You have to do what you have to do on the trail which means that the bag will spend some time crunched down. And when I get home I air it out and store it in the giant storage sack.

But, I'm assuming that what you really want to know is how small can a down bag be crushed without doing any permanent damage. And, as you asked, how long can it be kept compressed.

While I can't directly address the question of "how small can it be compessed", I can say that my bags sometimes spend alot of time compressed with no noticable degradation.

Last year I spent 4 months on a RTW (round the world) trip. Which meant that my WM Super Versalite spent alot of time compressed in the bottom of my pack. I took nothing that wouldn't fit in my 3600 cu in pack. While I don't use a compression sack I do compress it down fairly small. The bag also got used alot (which, in my opinion, may do more long term compression damage than stuffing - since you lie on top of the down crmpressing it essentially flat). I have since been on a couple of backpacking trips using that same bag and I haven't noticed any degradation at all.

I also have an older (25 year old) down 15 degree Northface bag. That bag has seen alot of action. While it is not as lofty as it was when it was new - it's still lofts up pretty darn well and is still very warm.

So, again, I'd say use the bag - do whatever you have to do (within reason) to fit it into your pack and, if my experience is any indication, even with alot of use (and/or alot of time spent compressed) your bag should last a good long time.

rionada