Down Sleeping Bag Question

[DanTaylor]

I have two sleeping bags, both are down. One is a 15 degree 600 fill and the other is a 20 degree 800 fill. Which would be the better cold weather bag? Maybe what I am asking is which would be the warmer of the two

[MuddyWaters]

The blue one

[Odd Man Out]

Fill power (600 vs 800) doesn't affect warmth per se. That is determined by loft. The fill power determines the weight. So a bag with 2 inches of 600 fill should be the same warmth as a bag with 2 inched of 800 fill, but the 800 fill bag should be lighter. However this assumes all other things are equal. But not all companies rate their bags the same way, so their be a differences due to quality, construction, age, condition, etc that could offset the theory.

[Time Zone]

I have two sleeping bags, both are down. One is a 15 degree 600 fill and the other is a 20 degree 800 fill. Which would be the better cold weather bag? Maybe what I am asking is which would be the warmer of the two

Multiple choice answers:
a) you have to test them out to be sure.
b) the temp ratings, if consistent, tell you that the 15 degree one will keep you warmer. 15<20
c) no, that's pretty much it. The 800 fill is probably lighter, maybe significantly.

extra credit:
the more interesting question would be, suppose the 20 degree one was 600 fill and the 15 degree one was 800 fill. Which will keep you warmer with overnight humidity peaking at 90%? [That's really quite common where I live in the southeast, near the start of the AT.] The issue? higher fill down may not loft as much under very humid conditions. Not sure how long it takes to be affected (one night, a few, several), but I think it's pretty well established that it does happen where it's humid.

[DownEaster]

If the bags aren't too old, they might have EN (European Norm) temperature ratings. These are conducted using sensor-equipped mannequins, one each to represent average male and female bodies. The EN figures should give "comfort", "lower limit", and "extreme" temperature ratings. The figure that matters the most to you would be the "lower limit" temperature (male counterpart to the female "comfort" rating). That's likely to be a few degrees different from the advertised temperature figure. For instance, my Marmot Cloudbreak 30 is marketed as a 30 degree bag, but it's actually EN rated at 32.4 degrees ("lower limit") and 41.4 degrees ("comfort") for comfortable sleeping temperatures for the average man and average woman, respectively. (The Cloudbreak 30's 4.5 degree "extreme" figure represents the lowest temperature at which a person could survive, though possibly with frostburn.) If you can get the EN temperatures for your bags you'll be able to make apples-to-apples comparisons.

[cmoulder]

If you trust the ratings, then obviously the 15deg should be warmer, but heavier. But shell/liner materials, zippers, etc are huge parts of the total weight... 20D vs 10D can make a difference of 6oz to 8oz, or even more....

And if you do trust those temp ratings I have a bridge to sell you in Brooklyn. :D

[BuckeyeBill]

The blue one

Reminds me when I had a set of quilts, all the same color on the outside but the winter quilts were red on the inside and the summer quilts were red.

[BuckeyeBill]

Winter quilts were blue. Need a new keybord.

[Venchka]

The EN, Euro Norm, testing procedure is specified online. DownEaster left out the mid-20s age, long underwear and R-5 insulation between the bag and ground.
It helps to list Maker, Model, internal dimensions, loft, side block baffle - yes or no, etc., etc. All bags are not created equal.
There's no substitute for personal testing and a reasonably accurate thermometer.
Wayne


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[Venchka]

When in doubt, pick the blue or red one. Grinning. Those colors have and are working well for me.
Wayne


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[MuddyWaters]

I was snarkily implying, theres not enough information for a meaningful answer.

[Feral Bill]

Try this: Fluff them both up, leaving and hour or so to fully loft. Assuming similar construction, the thicker one should be warmer.

[happypad]

So the higher number down makes it lighter?

[Venchka]

So the higher number down makes it lighter?

Not necessarily. I've been watching the specs for Western Mountaineering bags since the mid 1990s. Over the years their fill power ratings went from 700+ to 750+ to 850+ today. Always untreated. During that time the weight of the down, loft and temperature ratings remained the same.
The fill power of the down is not something that I consider in a sleeping bag. As a matter of fact, I consider the 700+ down (old testing procedure) in my 1994 bag to be superior to the 850+ down (new testing procedure) in my 2014 bag. Both are Western Mountaineering bags.
Wayne


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[Rex Clifton]

extra credit:
the more interesting question would be, suppose the 20 degree one was 600 fill and the 15 degree one was 800 fill. Which will keep you warmer with overnight humidity peaking at 90%? [That's really quite common where I live in the southeast, near the start of the AT.] The issue? higher fill down may not loft as much under very humid conditions. Not sure how long it takes to be affected (one night, a few, several), but I think it's pretty well established that it does happen where it's humid.[/QUOTE]

How fast were the trains going, again?


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[Venchka]

Insufficient data.
Loft, either top or total, have the most bearing on temperature rating.
Down fill power is unrelated to loft.
Here's a good place to start. Follow the links. The result of a few nano seconds of searching the internet.
https://backpackinglight.com/forums/topic/5625/
Compare the loft-temperature tables to the Western Mountaineering loft-temperature ratings for their bags.
On the question of humidity degradation:
Given the new testing to get down fill to 850-900 and up, by the time the down leaves the factory in a sleeping bag it is no longer able to meet the testing numbers.
Wayne


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[DanTaylor]

So the higher number down makes it lighter?
Actually, the two bags are only 2 oz. difference with the 600 fill bag being the heavier of the two.

[Venchka]

So the higher number down makes it lighter?

Bag A: 2 pounds of 800 fill power down.
Bag B: 12 ounces of 609 fill power down.
Which one is heavier? A pound of 650 down or a pound of 850 down?
Folks, down fill power is a marketing term. It's nice to know but it doesn't do a whole lot to make a decent sleeping bag.
I'll shut up now.
Wayne


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[Dogwood]

Given the two choices the 20* sleeping bag is a better cold weather sleeping bag....in the Bahamas.