Is there a discernible difference between a -20 and a -30 degree sleeping bag?

Question

Is there a difference between brands within these categories (when it comes to warmth and heat radiation that is)? Basically, if I show up in -30, or even -40, degree weather with a bag rated to -20, am I in a world of hurt?

Answer 1

I would say that you would quite be as warm as you would be if you had chosen the -40 degree bag. I think I would go for the -40 bag if you can find one.. just in case. At -30 to -40 degrees is that a chance you are willing to take??

Answer 2

A -40 bag is usually a bit more bulky than a -20 bag. Weight between the two is only usually a few ounces, but the volume a -40 bag takes up is much more than a -20 bag. So consider your manner of packing and how much room you will need to transport it. If you REALLY need a -40 bag chances are you will have a ton of other bulky clothing. So don't forget to bring a couple of Sherpas.

The lowest temperature I've ever slept in was -30. It was windy too, but I have no idea what the wind chill was. I had a -20 bag that trip and wasn't cold. I think I woke up once during the night when my face found the side of the tent. On another trip it was well below -20 with the wind chill and I only had a +20 bag. I wrapped my space blanket inside the sleeping bag and I wore a layer of fleece over my polypro that night. I woke up a bunch of times that night, but I mananged to get a few uninterrupted hours of sleep. I felt like crap the next day...which luckilly was the last day of the trip. It wasn't pleasant, but even a +20 bag performed moderately well in temps 40 degrees below what it was intended for.

Answer 3

Yes, there is. And I would not count on just wearing your clothes inside the bag. The more bulk you put inside the bag, the more compressed the bag becomes and the result is you will be even colder. The reason is the sleeping bag loft traps and warms air, and the air is what makes you warm.

Also, a brand new bag will perform much better than an old one for the same reason.

It also makes a huge difference what kind of insulation you have underneath you, for example a single foam pad vs. a winter rated Thermo-rest that's 4" thick. Or up on a cot, vs. right on the frozen ground.

Answer 4

While the one bag uses a higher 800 fill rating, the baffle may not be as thick. Therefore, a 650 fill bag with a larger/thicker baffle is going to be warmer than a 800 fill bag with a thinner baffle. If they had the exact same construction and thickness, yes, 800 would be just as warm but lighter. But that's probably not the case. I would say that the 600+ fill bag is probably thicker. [ADD] The ultralite backpacking crowd is nutters about weight. I've seen them argue about what type of thread to use when stitching a custom backpack to save fractions of an ounce. If you're like me, you won't care how much each specific item ways, as long as the whole pack remains under 50lbs.

Answer 5

I am sure there has been lots of studies on this aspect try backpacker.com. Different brands have different qualities of bags. I personally have a -20 degree mummy bag. It gets warm quick and stays that way.