Compression of down/synthetic

This cannot be considered by any means to be a test, but I can give you some actual data. My North Face Ultralight 0 deg 600 fill down bag (just over 11 years old) has been used, compressed, soaked by rain and spontaneous lakes, and stored in my closet. I use compression straps on the bag when on the trail. I have never washed the bag (it doesn't stink and doesn't look dirty, though I know it probably needs it). My bag when new had close to 5" of loft to it, but now it has about 4.25" of loft. That is a 15% loss of loft over the lifetime of the bag. It still puffs up nice and full when unpacked at camp, and keeps me warm down to around 10 degrees with a 3/4 length old-school thermarest + blue Wal-Mart foam pad. That I know of, my synthetic bags never lost any loft, but I hated them anyways because they were too bulky so who cares how much loft they had =P – My un-professional unsolicited advice is: wash if you grunge it up, pack it how you need to, and store it as fluffy as possible.

"Can you stuff it hard and just lay it out for a while to allow the loft to come back?"

No, not really.

When the manufacturer is trying to do a loft test on a new design, they will blow it up with air. A vacuum cleaner in reverse mode will serve here. That simply gets the maximum loft for measurement. As soon as you start doing anything practical with it, some of that loft will be lost, but it may not be permanent. A clothes dryer will fluff it up also, but you don't want to use much heat or else the fabric and stitching could be damaged.

When backpacking, I carry my down sleeping bag tightly bagged. But when I reach camp, I unbag it, shake it out, and keep repeating that several times before use, especially in a cold situation.

–B.G.–

The loft of a new back is over inflated. The loft of a bag after it has been used several times is it's 'true' loft. It keeps you warm just the same.