Down retains its ability to spring back for years, much better than synthetics. But if you think about it, no longer than your bag is compressed within your pack, you are going to do very little damage to it by stuffing it. The whole reason for these bags and their expense is that they do compress so you don't have to have an enormous pack.
I have mentioned before, the down sleeping bag that is compressed in a steel box under the ejections seats of fighter jets stays there for years before it is used, if ever, and springs to life to save that of the downed pilot, no pun intended..
There are only two kinds of people that understand Marines: Marines and the enemy. Everyone else has a second-hand opinion.
Gen. William Thornson, U.S. Army