Down Fill Power Impact on Quilt Temp Rating

Thank you so much Richard, this is the exact information I needed to work out how my old sleeping bag w compares to a new bag I am purchasing.
Your knowledge is greatly appreciated
Cheers
Shon

Richard do these #s come from the your apparent thermal conductivity vs down density? Or are they a result of some other empirical testing? Or….?
Those are some interesting results. It appears that one would only require ~5% extra down to cover the same temp differce for a 700fp garment vs a 850fp.

thanks,
James

James,

There are a number of separate studies that I combined to answer the question. None of which are related to thermal conductivity vs down density. The study that was most relevant was a private study paid for by a group of manufacturers for their personal use.

Five mummy bags were made exactly alike by the manufacturers and filled with 0.624 kg (22 oz.) of down. The only difference between the bags was the fill power of the down which ranged from 600 to 800 in.3/oz. in intervals of 50 in.3/oz. An EN 13537 certified lab was paid by the manufacturers to test the insulation value of each bag. The data showed that the bag insulation increased systematically with the fill power of the down in the bags. The bag insulation value increased about 0.1 clo for every 50 in.3/oz. increase in fill power.

Regards,

That's a very interesting relationship! I have developed a formula for loft vs. temperature using Western Mountaineering's published tables of their products. I use this as a guide when planning my down insulated projects. Of course, all their products use 850 FP down.

Using WM loft vs. temperature relationship and assuming that a quilt using say 900 FP is going to be 28.5% thicker than one using 700 FP (900/700), the temperature ratings would be 10 degrees different on WM's scale but only 4 degrees different based on 0.5 degrees per 50 FP.

That would mean that the lesser FP down would result in better value, whether in a DIY project or a store bought product. Hmmmmm.

I definatly agree w/ michael – if this is correct, the results impications are huge for our wallets.

Also, I appreciate the info you post here and really respect the effort you make to answer questions resulting from it. I wonder if it is difficult to post anything new since it means you will be swamped w/ questions (in addition to keeping up with questions from old threads).

With restect to the study you summarized….
I estimate that a mummy bag filled with 22oz of 800fp would be comfort rated to ~15F and thus have an average clo of ~8. Maybe the comfort temp is a little lower and/or the clo a little higher but the point I am getting at is, imo, the (+/-).1clo/50fp should only apply to the clos from the study. It is the % change in clo that would translate to other situations.

Now back on the results / conclusions from the study(ies)… I do have my doubts. Have you done any of your guarded hot plate testing, explicitly, fp effect on clo. I did find a posting you made (from the spectacular "A New Paradigm…") comparing guarded plate results for the MH subzero and MB Alpine jackets (see your post @03/20/2009 23:04:04 MDT ):
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=18950&disable_pagination=1
here you say:

"my laboratory tests showed that the MH Sub Zero jacket with 9.2 oz of 650 fill down was approximately 20% warmer than the MB Alpine jacket with 6 oz of 800 fill down."

to me this implies the Alpine would require ~20% more down to achieve equal warmth for a total of 7.2oz of 800fp. Also, if the Subzero contained 7.2oz of 650fp would be it would be about ~78% as warm as the Alpine with 7.2oz of 800fp. This is, of course, assuming same coverage of each jacket.
Now I know there are a lot of other things going on here (differt shell, down is probably fp tested to different standarts,…) but your testing appears to imply that the %change clo/fp is much larger than the study you summarized.
Are you able to resolve these two (maybe I am just missing something).

thanks, James

Also, sorry for dragging up something you posted over a year ago. I understand it is pretty tedious to try to keep up with all of this and understand if you don't have time/patience to go thru it

Edited to change 600 to 650 for the Subzero fp

"my laboratory tests showed that the MH Sub Zero jacket with 9.2 oz of 650 fill down was approximately 20% warmer than the MB Alpine jacket with 6 oz of 800 fill down."

9.2×650= 5980 cubic inches of loft.

6×800= 4800 cubic inches of loft.

5980/5 = 1196

4800+1196 = 5996

A difference of 16 cubic inches seems within the margin for other factors like material and construction.

Are we saying that 2" of 650 fp insulates better than 2" of 800fp? What's the discrepancy? The way the OP is framed seems confusing to me.

By saying that x-weight of 650fp insulates more than x-weight of higher fp implies that loft doesn't correlate to insulative value. Under what conditions were those tests done?

If the same weight of significantly different fp down were occupying a smaller volume than allowed proper loft, I'd expect that lower fp to actually insulate better.

Is the implication that equal loft of different fp downs insulates differently with the lower fp being superior under unrestricted (or marginally) occupied volumes?

Javan, your conclusions are only accounting for two of the three variables: Loft, mass, and fill power. Based on the quoted information:

9.2×650= 5980 cubic inches of loft.

6×800= 4800 cubic inches of loft.

yields (5980-4800)/4800=24.6% increase in insulating volume. This is consistent with the tested 20% increase in warmth of the lower fill power garment (given discrepancies in fabric used and potential thermal benefits of higher quality down resulting from less shaft).

EDIT: I had made a comment reiterating Richard Nisley's views on compressing of down. However after a bout of insomnia and many calculations, I believe there is a flaw in his analysis. Richard is correct in saying that clo/inch of down increases as it's density increases. The problem is that it does not scale at the same rate as the weight increases. So if your down jacket is compressed to 50% of it's maximum loft, it only loses ~25% of it's clo rating.