I am going to Aconcagua late in season (late February to early March), and was told to get a -20 degree F sleeping bag. I have a Mountain Hardwear Ultralamina 0 degree bag, and I don't really want to buy an expensive -20 sleeping bag that I might not use much. I have a rectangular 40 degree bag from Golite, and was thinking of using it with the Ultralamina instead of buying a new bag. I also will have synthetic insulated pants, synthetic insulated jacket, powerstretch baselayer, and down parka to sleep in if it were really cold.

Is using two bags a good idea, and Aconcagua is it really necessary with the kit I have? Thanks!

I've slept in -20 with a +20 degree bag and been fine with a down jacket and insulated pants on a Big Agnes air pad insulated with Primaloft. Was very cozy, but I tend to run hot.

I think Aconcagua is the best mountain for a combo bag system. The approach hike tends to be pretty warm and a -20 bag will have you sweating at night. I took a zero degree bag and a 25 degree bag. I slept in the 25 degree bag on the approach, the zero degree bag at Plaza Argentina (and then again at Plaza de Mulas) and then slept in both of them at 16,000 and again at 19,000 at White Rocks.

I did the two bag combo on my Aconcagua trip, a TNF Superlight 5 degree bag with an Alpine Designs summer bag over it. I was a little cold one night at high camp but nothing that the addition of my lightweight down jacket didn't take care of. And I do sleep cold. This was mid Feb. We summited on the 17th.

If you have big plans for the future, you might want to start watching for a deal on a -20 bag, though. I picked one up a few years later and have used it in the Himalayas and on Denali and have only been cold one night, at 14k on Denali. For me, bundling up inside a bag is uncomfortable and the clothes keep me from warming my likely cold feet against my skin.

JimS

Why do you need a -20F bag? It doesn't get to that temperature inside your tent. You can minus 15-20 degrees from the outside temperature if you have a four season tent and tent mate. From my limited experience climbing between 6,000-8,000m, I would take a zero degree bag. The difference between a zero bag vs -20/40 in terms of weigh and bulk is huge. Take into account that not all zero bags are created equal. You have a lot of clothes to compensate. Having said that, I have never slept in my heavy parka.

Back in 97/98 which was a really bad year on Aconcagua, I carried -5 F rated Marmot Goretex bag. We were on the Argentine route via Cerro Piramidal. The -5 F bag was good enough for some of the worst conditions I ever experienced in the mountains. The wind was strong, snow every day for three weeks. We went two of us, alpine style, so weight was extremely important. If you don't have many weight considerations, as someone commented above, two bags, one lighter one for the approach and one a bit heavier, would work well. If you will use mules to carry you gear for the approach, two bags would work just fine.

Andrew Rankine wrote: I have a Mountain Hardwear Ultralamina 0 degree bag... I also will have synthetic insulated pants, synthetic insulated jacket, powerstretch baselayer, and down parka to sleep in if it were really cold.

You should be fine with that above, no need for a second bag or a bigger bag. I've climbed Aconcagua twice and though on both occasions it got around -20C/-5F on summit morning (e.g.. 4am?) and windy, this was outside, exposed. As others said above, in your tent with a friend is warmer. And this assumes you will have decent mats underneath, probably an inflatable and a foam of some description.

Two bags can work for some situations, but only if they fit well together and one does not compress the down in the other. This goes for wearing a big parka in your sleeping bag too. A good down sleeping bag is probably the best insulation you will have on a mountain and wearing too many clothes in it can interfere with that process.

Ok, thanks for the help everyone. So what I am seeing here is that it could be a good solution, as long as the bags are not too tight of a fit that the insulation is compressed, though it may be overkill. I did forget, I have a Thermarest Neoair x-lite and a closed cell mat that I'll use. I could use my Exped Synmat 7 instead for extra insulation.

How do you like the Ultra Lamina 0 bag by the way? That was going to be my next bag. I do not get cold easily, I have a 20 degree bag and have been in temps down to single digits to the low teens and have been fine. I would think then the Lamina 0 would be great for sub 0 conditions?

So far the Ultralamina has been a great bag. It is very warm, but I have only been to about 20 degrees in it so far. Though I was in a hammock which significantly decreases the warmth of a bag.

I used it this summer in Europe and was great early season in the Tyrol and German Alps, and later in season I found it to be pretty breathable in warmer weather too.

The features on it are nice, like the dual zips down both sides that allow you to sit up in the bag. Not sure how the new model compares to mine, they were updated I think.

I agree with others that a high quality zero degree bag by itself plus clothing should be sufficient. And I would consider getting the NeoAir xTherm model which is a lot warmer (R5.7 vs 3.2) than the xLite and only a couple ounces heavier. That way you can avoid the extra weight and bulk of the closed cell mat as well as that of the summer weight bag. Another consideration is that if you take a tightly closed nalgene bottle of hot water to bed with you it almost doesn't matter what the rating of the bag is, you will sleep very warm.