View Full Version : Question about down fill and temp ratings

01-03-2011, 22:23
I'm on the market for a new sleeping bag. Currently comparing two models: Kelty Light Year 40 and Kelty Cosmic Down 20. The Light Year is 650 goosedown and rated at 40, where as the cosmic is 550 goosedown and rated at 20. I always thought the higher the fill, the lower the temp. Is this not true?

01-03-2011, 22:37
The fill number is basically how much volume an ounce of that down will occupy. The higher the number of fill, the less down you need to achieve the same loft which means a lighter and more packable bag.

01-03-2011, 22:44
the fill number of the down has nothing to do with the temperture rating of the sleeping bag. The higher the number, the better the quality of the down. The number represents how many cubic inches one ounce of down will displace. So a 550 fill bag would be less compressable and possibly heavier than a 650 fill bag. You'll also notice that bags with a higher fill number are much more expensive. But you can have a 550 fill bag and 650 fill bag to be made to the same temperature rating. These days its possible to find bags with 800+ fill ratings.

01-03-2011, 23:17
Going along with my previous question, is a rated 40 bag going to warm enough for a future thru?

01-03-2011, 23:19
Also, by the way I sleep in a hammock and use a sleeping pad.

01-03-2011, 23:36
In the order you asked you questions Spider:

NO. Not true.

Probably not. A 20* sleeping bag in a hammock during the typical 3 seasons when the AT is thru-hiked is more in line with the norm, based on the info you provided.

01-03-2011, 23:55
I'm glad I had my 0 degree bag at the beginning of my thru, I will say that. I use a 0 degree synthetic now, just for the emergency factor. I was always careful with my down bag, but if it gets wet in freezing weather, it can kill you. Synthetic bags are getting better and lighter all the time now.

01-04-2011, 00:16
I am familiar with the WM range.
The Ultralite , rated at 20f and pretty accurate for me, has 16 oz of 850 down.
The Kelty Cosmic 20f bag has 18oz of 550 down so it sounds pretty optimistic to me.
( 850 to 550 = same loft with ablout 50% less down)
BTW, the usual rule is that the cheaper the bag, the higher the claim.