:...I seem to remember a specific article on here, maybe as many as 10 years ago that had specific numbers for the permanent loss of lost when "over-compressed" with numbers like 20-30% reduction in loft after a *single* over compression. Possibly I'm remembering the results for synthetics,..."
I do not doubt that. I remember flipping through and reviewing an article like that. I do not remember the date on it though. Anyway, it struck me that they did not shake the bag thuroughly and wait 30 minutes or so for it to regain it's loft. In a later article (I believe it was Ryan's) the author went on to discuss loss of loft due to moisture take-up by down, ie, dampness. But again, the shaking and mechanical lofting was not done to any effective degree.
Yes, I agree. Synthetics, such as holofill and varients, will kink permanently when compressed around 5 to 1. Finer fibers are better, more flexible fibers are better, as are some additives to the plastics to cause them to have a memory of the origonal extruded shape. But they only last 3-5 years, unless you are a zeolot about keeping them uncompressed. The synthetic fibers are mostly based on holofill.
If damp, a bag may take up to 2 minutes of shaking to seperate compressed down. Often in the summer, I have gone to bed with it damp and woken up with it dry and fully lofted again, by morning. If it is fairly dry, about 30secs or less will do OK. Use your own judgement.
In any case, a down plume, once compressed, can be as small as one or two percent of the origonal fully opened plume in area. Theoretically, you should be able to acheive about 50:1, but down will resist you more and more as you compress it further and further. About 10-20 pounds on each strap will compress my bag and jacket enough to fit into the small pack. This is around 15:1. Damp it may go much easier, but I go more by size than compression ratios.
Compressing will squeeze air out, often overlapping these fibers into a compressed sheet. They will tend to stay that way due to the micro-fibers gripping each other. Shaking will mechanicaly move these out to the more natural plume condition. Basicaly, it increases loft considerably. I would guess a good 100-400% over an unshaken bag depending on humidity and dampness. Heat, just your body heat, will tend to "straighten" these fibers, too. Hence, the increasing loft over the course of the night.
If you hike 10 hours a day, a relativly high milage day of around 20mi at 2mph, this means that 12-14 hours are left for the bag to regain its loft before being compressed again. Down WILL regain as much loft as it can, given the conditions, over about 30 hours. But, 14 hours is only like 1 geometric progression away from the first three, starting at about two hours. Once shaken out and laid open (assumed to be in a dry area like under your tarp) it will continue to regain loft for about 30 hours. But, I normally use mine before that happens. Continual use, as in a through hike, introduces dirt and body oils which I never figured but alow for with my jacket. This has another 4oz of down in it and will protect my core.
One good way to minimize body oils is to use a light set (minimally) of long johns. I usually rinse these on a good hot day in a stream somewhere and put them hanging on my back pouch to dry as I hike. Nope, never lost them in over ten years of doing this. Sometimes I put them on and go swimming. Or, wear them into a shower.
There are lots of tricks you can play with down. Mostly, keep it as dry as you can, and, as clean as you can. Shake the hell out of it after compressing it. It really doesn't hurt it.
Note: That was for good down. Less expensive 550-650 fill down has a large percentage of downy feathers. Compression of these is like compressing holofill.