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Looking ahead to winter.
Does anyone have an idea of how to guage temp ratings when combining, for instance, a sleeping bag and a quilt for winter use?
If I combine a 20 degree down bag with a 20 degree down quilt, what sort of temp rating can I expect? Let's assume that both the bag and the quilt each have 2.5" loft of 800+ fill. Anyone seen discussions on this topic?
Mike
Yes, from what I have read here, the general consensus is that you add the lofting capacity of both items, and use that as a gauge for how low in temps it should go.
One thing to watch is that the top item may compress the lower item to a certain degree, by its weight of laying on top. This can cause a lower loft total to be realized in the real world usage.
As it happens I researched this just recently. IIRC, you subtract the rating of the outer layer from 65F, take half of that, and subtract it from the rating of the inner layer. For example, Tim M is making me a 45F quilt, (65F – 45F)/2 = 10F, so theoretically I should be able to take my Summerlite down to 32F – 10F = 22F. That's assuming an adequate pad and no fill compression.
Tom and Will, thanks, this is exactly the info I need.
So the math is for my example is 65-20=45/2=22.5. Then subtract 20 = 2.5 degrees.
So now I am wondering why these 5 inches (at best) of loft is 2.5 degrees and an WM Ultralight, which has 5 inches of loft and is, according to all reports I've read, a very conservative 20 degree bag??? Have I done the math correctly?
As far as I know, there is no bag with 2.5" of loft that comes anywhere near 20 degrees in the real world.
So the problem may not be with the math, but with the assumption that 2.5" of loft will get you to 20 degrees.
The WM bag with 5" of loft IS a good bag for 20 degrees, and is well proven.
I would say that a total of 5" loft should get you to the same temps, or thereabouts.
“Have I done the math correctly?”
It appears you have.
For example, a WM Kodiak is 7” loft at 0F. But that’s total bag loft. Cut it in half for top loft, or 3.5”.
So the top loft of your total system is about 5”. So you could probably expect your 2.5F performance if you have a warm pad.
With those cold of temps, I always try in my backyard first (with high winds).
-Barry
Tom & Barry, those are good points and suggestions. Both the down bag and the quilt are rated for 20 degrees, but I have always had my doubts. Hard to tell cause I'm a cold sleeper. I will try several combinations in my back yard (excellent suggestion) and work in insulated clothing too to find a system that keeps me warm. Cheers, Mike
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