I have been searching forever, I know ive seen it but I cant find it. How much loft equals how much heat? Loft and temperature ratings? trying to get an idea on how much down i need to buy for the quilt im going to make.

thanks
Jeff

Jeff, there is no simple answer. Some of the best minds in this field disagree. Witness this thread, it contains the estimations you are looking for:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=5625&disable_pagination=1

My advice is use the single layer loft/temp ratio of a respected bag maker such as Western Mountaineering, Feathered Friends, or for a comparable bag at lower cost, Montbell. This comparison would be reasonably valid if you are using comparable fill and bag shape.

Here is a table for Western Mountaineering lofts. They are double layer lofts (top and bottom added together) so if you halve the values you have an idea of what is needed just on top.
http://www.westernmountaineering.com/index.cfm?section=Products&page=Sleeping%20Bags&viewpost=2&ContentId=27

Edited by pappekak on 03/21/2007 21:49:39 MDT.

Great thread Brett, thanks.

How about ounces to loft thickness?

quoted from thru-hiker "800+ fill power means that one ounce of down will occupy at least 800 cubic inches."

So how much loft would that be spread out over 800 cubic inches?

Thanks Steve. My brother just got the Bison for his upcoming trip to Denali(lucky). I have to say that is the best sleeping bag I have ever seen, just hurt his pocket book alot.

800 cubic inches is a measure of the volume the 1 ounce of down occupies. Therefore, if you had a baffle compartment had an area of 20 inches by 20 inches (400 inches sqaure), an ounce of 800 fp down would give that area a loft of 2 inches (400 in^2* 2 in= 800 in^3). If you have a quilt, like the JRB No Sniveller that is 48"x78" and want 2" of loft, then you find the volume that you will be filling and divide that by the fill power of the down (ci/oz) to find the amount of down (in ounces) that would be needed. So in the case of the NS, 78*48*2=7488 ci. 7488/800= 9.36 oz of down. They use 10 oz of down to really puff it up and give it a bit of an overstuff.
I made a down quilt last weekend actually and wanted it to be good down to about 30-35*. After looking at all the specs of a variety of quilts and lightweight bags I decided I would be fine with 2" of loft. My quilt had a volume of 7068 ci, so I would need 8.8 oz of down. I ordered 9 oz to account for loss while I was stuffing.
I hope this helped clear things up a little.

Adam

perfect Adam. Sometimes reading all these oz/loft/in/ci and so on just drains my logical thought process. Thanks for shedding some light