View Full Version : Sleeping Bag Question

01-15-2011, 13:48
Plan on returning to Hiawasee/Dick's Creek mid to late Feb and rethinking my sleeping bag situation.
Currently have a Golite 20 degree Mummy Bag with 800 goose down fill. Also, have a silk liner for it and can/do wear clothes to sleep as weather dictates.

Thinking that maybe I need to go ahead and get a Down Bag--Zero temp to get me throught the Smokies and into the end of March.
Question is ---when I look at bags like the Campmor Goose Down Zero bag or the North Face Mountain Superlight Down Sleeping Bag--also Zero temp---they are listed at 550 and 600+Eastern European goose down insulation.
So will I really notice much of a difference in my existing bag with 800 fill and either of these two bags with less goose down insulation but are listed as Zero temp bags.
Please explain and offer suggestions. Thank you.

01-15-2011, 14:25
I think 800 fill down just uses less down to achieve that rating. The difference between a 550 fill bag and a 600+ fill bag is the 600 uses less down which means it should be lighter. Not sure though.

01-15-2011, 14:37
The higher the number the better the insulation factor = the less down they need to use = lighter/more compact bag for you.

500 fill would be like a less then mid grade fill ( think 85 octane gas) - some quills in it
700 fill is decent mid grade (think 89 octane gas) no quills but not the top of the line down
900 fill is great and cost $$ to get. (think 103 octane racing fuel)all down no bits of "filler" from other parts or feathers in it. Holds heat and insulates better then the rest.

If you have a 500 fill bag rated at 10 degrees, it might weigh 6.25 pounds. it might compact down to the size of 2 soccer balls.

If you have a 800 fill bag rated at 10 degrees, it might weigh only 2.75 pounds and compact down to the size of a football.

Jim Adams
01-15-2011, 15:02
The down rating actually applies to the size of the down (feathers) therefore 550 having "larger" feathers takes more space and won't compress as much as 800 which has "smaller" feathers. If they are both rated to 20* the 550, 600, 700, 800 or 900 rating will all be a bag rated for 20* but the size, weight and compressability as well as price will be different between each bag. I believe the number refers to the number of feathers that will fit in 1 cubic inch.


Jim Adams
01-15-2011, 15:05
BTW, I would definitely use a 0* at that time of year and your destination. I used a 0* in mid March from Springer to Damascus and was far more comfortable than when I used a 20* bag.


01-15-2011, 15:34
So will the zero degree bag be that much warmer than my twenty degree bag? In other words does the 800 fill versus the 600 fill really impact the temperature confortable. Because my 20 degree bag has the higher # in reference to the down fill.
Just need to understand if it just relates to how small it can be compressed or also the actual temperature issue.
Thanks again.

Jim Adams
01-15-2011, 15:36
A 0* bag is assumed to be comfortable to 0* no matter what fill it has.
The difference is in weight and packability.


01-15-2011, 15:43
Loft and cut are the two major factors in sleeping bag warmth. Ounce for ounce, 800 fill down will give you a lighter bag of the same loft. Simply laying out your old bag against one that you are considering should tell you how much warmer the new one will be (not exactly degree-wise, but you'll get some idea). Some bags have more loft on top than they do on the bottom, figuring most folks won't turn the bag over while they sleep. Factor this in, too, as the top of the bag (plus your sleeping pad)is really what keeps you warm, since the bottom gets compressed under your body weight, effectively negating whatever loft is there................................or something........:D

01-15-2011, 16:10
Just want to say I like your user name Tawa

01-15-2011, 16:42
So will the zero degree bag be that much warmer than my twenty degree bag? In other words does the 800 fill versus the 600 fill really impact the tempe

Oh, yes. The temperature rating comes from the loft -- how many inches of insulation are between you and the cold air. 800-fill down provides more loft per ounce of down, so you need less down for the same loft. But a 0-F rated bag will be significantly warmer than a 20-F rated bag.

So if you compare the same temp ratings, say for a zero-F rated bag, a 600 fill bag will weigh a little more than an 800 fill bag. Same with 20-F bags, a 600 fill bag will weigh a little more than your 800 fill bag (all other things being equal, which of course they rarely are.) The fill rating does not affect the temperature rating, it only affects how many ounces of down are needed to gain that temp rating.

Make sense?

01-16-2011, 00:59
Actually, thermal conductivity ( or R values) data for down of different fill powers and sources are in rather short supply. In effect, the data to explicitly answer your question is scarce.

Tradition long has it that the insulative value of a lightweight insulation such as down and down feather blends depends only upon the thickness.

You can download a lot of data on reported loft (thickness of sleeping bag) and reported temperature rating. You can also download or copy data which includes bag weight and sometimes the down filling weight as well.

Sometimes, if you plot this all up, you get a general idea of the temperature rating from from just the loft data, and manufacturers do often appear to be using the same general data. Wtih enough work, you can get the data for bag weight and/or fill weight vs temperature rating as well.

IF that loft hypothesis is indeed correct, then you should see that --- for the same geometric factors such as mummy bags vs rectangular bags ---- a down sleeping bag made with lower fill power down will be heavier (more fill weight) than a down bag of higher fill power.

In actuality, down which is slightly compressed has a lower thermal conductivity than down which is fully fluffed. But, the thickness is decreased because of the compression and the R value of the compressed insulation decreases, and it could turn out to be that the net insulative effect is increased, decreased or remains the same.

The data that I have indicates, from literature searches, that the net insulative effect of down compression is a decrease. Others have made other claims, but the data driving these conclusions is indirect, not direct.

There is absolutely no truth to the claim that the fill power of a down/feather blend represents the size of the feathers.

If you want the information on down fill power, there is an International Down and Feather Laboratory (www.idfl.com) that publishes standards for down products. You can see some of their articles at http://www.idfl.com/articles/

You won't exactly find thermal conductivity or sleeping bag warmth as a function of fill power there.

This is not to say that at least some makers of equipment do not have data on the thermal conductivity of various down products, but that they don't publish it.

01-16-2011, 13:38
FWIW, I was happy with a 20F rated bag going through that area this past March, but I had a good down parka and down booties to wear inside the bag. My feeling was that I wanted to pack to be comfortable down into the teens, and be "survivable" of course some decent interval below that. If it got too much down from "comfortable" into "survivable" I would consider getting off trail for a bit, but never had to do that.

Of course there are a lot of variables, what works well for one person (and one brand of sleeping bag) might not for another.

And if you don't particularly want the warmer clothing otherwise, it certainly is more weight efficient to have a loftier bag than more puffy clothing, but I really liked having warmer clothing to wear in camp, to be able to get up in the night and in the morning and still be reasonably warm.

01-16-2011, 21:16
Your pad will be as important as the temp rating on the bag.

01-16-2011, 23:02
Your pad will be as important as the temp rating on the bag.

This is often overlooked. Sleeping pad choice will determine, to a great extent, how warm your bag will be (example: Take a 15 degree bag out on a 15 degree day with an air mattress [no insulation] and you will freeze).

01-17-2011, 12:31
Love the Montbell SS UL Hugger #1 with a Sea to Summit Liner worked great from me in the NE in late Dec

Zeno Marx
01-27-2011, 19:17
Shape is a really, really big deal for some people. I've known a person or two who went out and bought the top-of-the-line, highly designed bag with extreme mummy tapering and found it was claustrophobic and very uncomfortable. They didn't realize how much they need to move around and not feel confined.

Also know some hunters who will only sleep in the old style rectangles. They're big guys, but man, all that wasted space in the foot area makes me chilly just thinking about it.

01-27-2011, 19:29
the campmor 20F is a great value but when you go to a 0 bag you want the 700 - 900 fill down for hiking. The basic bags are heavy and bulky

01-27-2011, 22:11
I am in a bit of the same dilemma.. Currently have a 15 degree bag, but it isn't down. I am thinking of going for a 0 degree bag filled with down to leave mid March. Although I am on a budget which is narrowing my choices much more than I would like. It's been my most difficult piece of gear thus far... hope you have some luck with yours...