I can't really find too much really technical information of value about down, its volume or "fill power". TNF site says that one ounce of down fills one ounce of volume fully compressed and that one ounce of 900 down will expand to 900 cubic inches. So it sounds like the specific gravity of fully compressed down is 1.0 like water which sort of makes sense so lets accept that. But it also sounds like they weigh one ounce of uncompressed down and stick it into a large graduated container with no weight on it and eyeball it to see where the top is. What I wonder is for instance if this say a 9" diameter cylinder and they put one ounce of weight on it (including the weight of the cardboard disc), the area of a disc being pi x r x r, or 3.1 x 4.5 x 4.5 or 63 square inches, thats .016 ounces of pressure per square inch, what would the new volume be? Since all down IS stuffed into a shell and since it is the pressure against the shell that makes it fill, then we have to assume that there is some pressure in all down garments and the down will not loft to its full lofting capability.
My old REI down jacket dropped into a cardboard box sort of lightly so that it is pressed a bit on the sides, enough to say assure that most of the air space not in the jacket is closed, balanced against the fact that the jacket itself has some "lofting" to it, I measure a volume of 8" x 12 x 20" or 1920 cubic inches. I sort of think based on a big TNF coat of the same era having 9 ounces of fill that this jacket has at least 4, maybe 5 ounces of down, say five ounces of 550 down. It may be 600 down and it may only 4.5 ounces of it but it sort of averages out similarly. Then negating any volume of the jackets nylon shell, that would be 384 cubic inches per ounce after being in the dryer for a few minutes to loft it, and the jacket has a thickness of about 1.25 inches, or 1.5 inches where there are larger "bags" for the down since it has sewn through construction. Since baffled construction has that icky "weight" and time consuming construction, I'll assume that most jackets vs coats have sewn through construction and therefore have more pressure against the down near the seams. So assuming all of this it appears that the down in the jacket is exhibiting and effective loft power of" 384 vs Say 600, which would be 64% of its rated "full loft power".
Glenn was looking at a WM jacket with 3.5 ounces of 850 down so that should be 2975 cubic inches under no pressure and should have a loft of 2975 / 1920 times the thickness of my jacket or 1.5 times more thickness, or 1,9 to 2.3 inches of thickness measured laying on a flat spot. I wonder if that is true, and if Glenn gets that wm jacket if he'll measure it for us. The photos do not appear to bear this out. It looks like the flash has less loft than my jacket. This tells me that the stuffing pressure of down garments is FAR MORE CRITICAL TO THE GARMENTS VOLUME THAN THE ACTUAL "LOFT VALUE" OF THE ORIGINAL DOWN. aLSO i WONDER IF THE HIGHER LOFT DOWNS ARE COMPRESSED MORE BY THE SAME AMOUNT OF PRESSURE ON THEM, MEANING THAT LOFT NUMBERS ARE REALLY MARKETING AND DETERMINING NUMBERS RATHER THAN AN INDICATION OF THE WARMTH OF THE GARMENT. iT IS SAID THAT THICKNESS= WARMTH, HOWEVER SOME MATERIALS MAY HAVE A HIGHER R VALUE PER INCH.
JUST SOME THOUGHTS
jIM