Hate to say it depends, but it does. Some synthetics and lots of down bags do not reexpand well after long storage compressed. Like hikermor, I have seen some good down bags that come out OK in a few hours. The old GI vacuum packed down bags (for seat pack survival kits) were pretty much worthless when opened (don't ask me how I know, just say I was glad to have an excellent parka that night). I have also had problems with lots of synthetic bags that would not expand well after months to years of compression. The newer Wiggys bags (like yours should be Chaosmagnet) have stayed vacuum packed for several years and came back to 90% within a few hours of opening. Check out the Wiggy's website wiggys.com for more information. (The usual disclamer here, just a very satisfied customer, several times). This is one reason they are the only bags I will use in a stored kit. If practical, I still do not compress the stuffsack if I can help it. In cold climates (not here >-() I carry one in my car in the sack supplied, but I do not compress it.

Respectfully,

Jerry