Are two bags warmer than one??

[Creek Dancer]

So the plan is to hike up to Le Conte shelter this weekend with a friend of mine and spend the night. The temperatures will probably get down to the teens and possibly single digits at night. The problem is that my SD bag is only rated down to 15 degrees. I’ve only used the bag down to about 30 degrees and I found it to be just right at that temperature. I am a cold sleeper. I really can’t afford a zero degree bag right now. I also have a 32 degree WM bag. If I use both bags at the same time, by putting the WM bag inside the other bag, will I get any added warmth? Does it work that way? I am going to freeze my arse off? I appreciate any feedback. :-?

[highway]

Add your clothes, In cold weather long underwear, top & bottom, plus whatever jacket you wear for warmth too, with hood, hopefully, wearing it too, covering the head well.

I bel,ieve I would go for that and the 15 degree bag, instead of toting the second bag. Since you already expect cold, you will already be wearing some combination of the above, so sleep in the clothes. That is more than enough extra margin for comfort.

[jlb2012]

What I usually do when using two bags is to just spread the second bag on top of the first like a quilt - that way the loft of the second bag won't be compressed like it might if you use the second bag inside the first

[saimyoji]

This question has been asked like three times now over the past couple weeks. It would be good to know some kind of formula on combinations of bags/liners. Of course it will differ depending on the bag, but in general how much does a second bag lower the temp. rating?

[Kevin A. Boyce]

Well you will lose some loft in the WM bag from stuffing in the other bag, so that is a consideration to factor in. I would suggest you bring along another sleeping pad a lot of your heat loss is via the ground.

When I winter camp, even if there is no snow, but the temps are at the levels that you mention, I bring along both a closed celled pad and an open cell pad. The Ridgerest goes on the bottom, the Thermarest on top. You may want to bring a piece of plastic/tyvek for a ground cloth if in a shelter as they get drafty... It adds a nice barrier but not totally needed.

[Creek Dancer]

Great ideas. I use an InsulMat pad, but I will also bring along the Ridgerest too. The WM bag only weighs a little over a pound, so I think I will bring that as well and use it like a quilt as HOI suggested. I did try to put the WM down bag inside the SD synthetic bag and it didn't seem very tight. The SD bag is one of those "flex" bags, so I think that helped with maintaining the loft.

Or I could just steal my friends sub zero bag and make him freeze off his arse instead. This was all his idea anyway. :D

[copythat]

http://www.whiteblaze.net/forum/showthread.php?t=18174

[Gray Blazer]

I was wondering about this anyway, and maybe this is an ignorant question-Could you use a 55 gallon industrial garbage bag and put it all the way around your sleeping bag for extra insulation? It wouldn't weigh much and wouldn't take up much room. Any opinions or experience out there with that?

[jlb2012]

I would suggest instead using the plastic bag as a vapor barrier assuming it is cold enough - putting it around the sleeping bag would tend to cause the sleeping bag to get wet and possibly lose loft

[scope]

Loft is overrated when you're talking about putting a bag in another bag. The top bag acts as an insulator to the inner bag so that the inner bag works more efficiently even if there is a loss of loft. Not so if completely compressed, but that shouldn't be the case. I can vouch that this system works.

I use my 20 degree bag inside my summer bag, and I suspect that this is the most effective way to do it - lighter bag as outside layer. I think the physics of how a bag absorbs and retains heat is the main reason for this, but many summer bags are cut wider (and winter bags cut narrower) so that any loss of loft would be minimized.

[scope]

I would suggest instead using the plastic bag as a vapor barrier assuming it is cold enough - putting it around the sleeping bag would tend to cause the sleeping bag to get wet and possibly lose loft

I've been curious as to how a bivy would work as an outside layer instead of another sleeping bag. Since its breathable material, that should help retain heat like a vapor barrier without getting too wet inside, right?

[WalkinHome]

The Navy SERE (Survival, Evasion, Resistance and Escape) instructors had us use one extreme cold weather down bag inside another and it was toasty even though it was -20 around us. Had on just underwear. So if you want to use two bags it can work. Don't know of any formulas though. Don't forget the boiling water in the nalgene trick-it works. Be sure the top is screwed on tight and not hung up on some ice that will melt and allow the bottle to leak.