So I'm trying to decide between buying a 0 degree bag and a -20 degree bag.

I do a lot of backpacking and a fair amount of semi-serious mountaineering, and because I live in the inland northwest, much of this involves sleeping out during nights where temperatures are between 20 and 45 during pretty much everything but the height of summer. I already have a 15 degree bag that works well for most nights in this temperature range, even though it's getting old and has lost some loft. With this bag, though, I'm usually good until about 25 degrees (where I have to sleep in it wearing a few layers) or even 20 degrees if there's little to no wind. However, I've just recently had a few 10-15 degree nights, and these have been genuinely uncomfortable to the point that I was legitimately worried about fingers and toes come morning.

Hence, the new bag. I don't intend to make a frequent habit of sleeping out when the temperature is below 15-20 degrees, but I'd like to have a bag in which I could comfortably sleep wearing only my base layer between, say, 10-30 degrees (and use my old bag for anything warmer). I'd also like to be able to feel safe if I *did* get stuck outside on a night I thought it would be more like 15 and it ended up being 0-5, though this would be something that would happen rarely, if at all.

So on one hand, this makes it sound as if a 0 degree bag would be perfect for me. On the other hand, I've frequently heard (including from the guy at REI today) that you should always buy a bag that's rated for 10-15 degrees colder than the temps you're planning on using it for, AND I'm a cold sleeper who doesn't sleep well on his back and would absolutely not mind paying another $100-$150 to have the ability to sleep in a partially-zipped bag in his thermals only in 10-15 degree weather. So now I'm thinking that maybe getting a -20 bag isn't as ridiculous as it seemed to me at first. On the other hand, I don't want the bag to be so hot that sweat into it when it's 20 degrees out and then am soaked for the rest of the night.

So that's all to ask:
1) Will a 0 degree bag be only a little warmer than a 15 degree bag, that it's not worth paying another $300 just to basically tread water in terms of my ability to be comfortable during rare high-altitude/high-wind bivies?

2) Will a -20 degree bag be so absurdly warm that I wouldn't actually be able to use it for 20-25 degree nights and would waste a bunch of money to end up still having a gap in between 10 degrees and 25 degrees where I had no bag that allowed me to sleep comfortably?

If it helps, I have an MSR AC Bivy and a Sierra Designs Zolo 1 that I alternate between depending on the conditions and how comfortably I want to be able to sleep on any given trip.

Thanks for any help; I've already talked to a number of really helpful employees at various gear stores about this, but I'd love more feedback before I put the money down.

locke456,
Go with the negative two dime bag. In the long run, you won't regret it (I went -20 over ten years ago and have never had second doubt)...
Also, go with down. It's expensive yes, but will serve you well over the years.
Good luck out there and stay warm..
JM

Some thoughts:

That guy at REI probably has never climbed a significant alpine route in his life. I don't know a single successful alpinist who brings a warmer bag than he needs.
Sleep in all your clothes. If you are not wearing all your clothes to bed, you brought too many or too warm a bag.
Change into dry socks at night
Drape your puffy belay jacket over the top of your bag, this way both the parka's and bag's insulating is not compressed.
Make sure you have good ground insulation
Jesus is correct, a good down bag is more money up front, but one of the best investments you can make for a quality night's sleep. My Western Mountaineering is 17 years old and still going very strong, after many, many nights.
Bring a tightly sealed bottle of hot water in your bag when you go to bed.
Not all bags are created equal. A +15 Feathered Friends or Western Mountaineering bag may be as warm as other big brand name bag's 0 degree bag. Using a 0 degree FF or WM and the above techniques you should sleep very warmly in the coldest of your anticipated nights.

EB makes good points.
Whatever way you go, the most important thing is to get quality down fill and shell out the bucks for the best possible quality manufacturer. That way, you will never have to upgrade.. You wanna be in your seventies still climbing peaks and sleeping in the thing (treat her well)...If time is on your side, wait until summer for some sales on winter bags.
FWIW, I roll with a Marmot Col. It's not the "best" -20 bag out there and it wasn't my first pick. But I got it on a killer pro/bro deal, so it's been a great value with many, many comfortable sleeps in the cold (and yes..I have gotten sentimental with the thing and I do love it now..oops..TMI)
also:
Here's a WM negative dime bag (split the difference)
http://www.westernmountaineering.com/in ... ntentId=42

locke456 wrote:I already have a 15 degree bag that works well for most nights in this temperature range, even though it's getting old and has lost some loft.

Is this a down bag, or a synthetic? If its a down bag, it hasn't lost its loft, the loft has simply clumped due to the oils in your sweat seeping into the bag, along with other dirt and grime. Wash it, very well, with down wash from Nikwax or Revivex in your bath tub or a good quality front load machine. That may restore your bag to near newness.

locke456 wrote:I don't intend to make a frequent habit of sleeping out when the temperature is below 15-20 degrees, but I'd like to have a bag in which I could comfortably sleep wearing only my base layer between, say, 10-30 degrees (and use my old bag for anything warmer). I'd also like to be able to feel safe if I *did* get stuck outside on a night I thought it would be more like 15 and it ended up being 0-5, though this would be something that would happen rarely, if at all.

I've backpacked for years. One of my first forays into winter mountaineering was done using a -20F down bag, when conditions were expected to fluctuate around 0F.... I heard the same thing "if you sleep cold..." Well, I do sleep cold. Except for that trip. I SWEATED MY NUTS OFF! The first night was 20F for the low, and I was roasting. I had the bag fully unzipped, and I woke up too many times to count. The second, third, and fourth nights though were much colder, closer to 5F, and I was comfortable then, but I could have slept just fine in a 0F bag too... And I would have saved myself nearly 2 lbs of sleeping bag too.

locke456 wrote:So that's all to ask:
1) Will a 0 degree bag be only a little warmer than a 15 degree bag, that it's not worth paying another $300 just to basically tread water in terms of my ability to be comfortable during rare high-altitude/high-wind bivies?

2) Will a -20 degree bag be so absurdly warm that I wouldn't actually be able to use it for 20-25 degree nights and would waste a bunch of money to end up still having a gap in between 10 degrees and 25 degrees where I had no bag that allowed me to sleep comfortably?

I have a huge collection of sleeping bags. -20, 0, 15, 32, all down, and then a few synthetics that are more or less loaners or for really wet camping trips. I have never regretted having a 0 bag in the mix with my -20 and 15 (both of which I owned prior to buying the 0). I firmly believe you will be too warm in a -20, plus the extra weight is not worth it most of the time. You should always carry a puffy with you for winter trips like this. If its a big puffy (think MH Sub-Zero, Absolute Zero, Chiliwave, etc) then drape it over the sleeping bag for extra warmth. If its a small puffy (MH Ghostwhisperer) wear it in the bag. I always make sure I go to bed with socks that I dedicate to sleeping in only (they never go in my boots during that trip). I always wear baselayers in a bag - they help keep the bag clean, as well as moving moisture away from your skin, and that keeps you warmer as well. I also bring a wool hat, and lightweight gloves, which I will use in my bag as well for really cold nights.

I think the best thing you could do for your weight, and wallet, is get a zero DOWN bag (I've always felt my down bags were warmer than the synthetics rated the same), and use two pads - a closed cell foam, and an inflatable, like the new Neolite X-Therm (I own this, and it is awesome in weight and warmth). The reason for two pads is simple - a closed cell can't provide enough insulation from the ground on its own to keep you truly warm. And an inflatable may kill you if it springs a leak, as it has zero R-value when its not inflated, and sleeping directly on the ground with no pad is the quickest way to loose heat in a sleeping bag. Plus, both pads together make a nice comfy platform, and comfy = more rest.

Let me know if you have any other questions.

ProTip: Boil some water and throw it in a Nalgene and a bottle-cozy for a nice hot water bottle. Your comment about feeling safe - unless you're hit with a nasty blizzard, an additional 20F of temperature being lower than expected should never worry you. Between making a hot water bottle, and your additional clothing (puffy, softshells, mid-layers), you should be able to weather those conditions safely, if not even comfortably.

TI

All these comments are really helpful, so thanks! My current bag is a Sierra Designs Gobi 600 (so, down) and I'm absolutely sure now that it just needs a wash; I used it a few times last summer when I absolutely didn't need a bag at all and sweated into it quite a bit. So, thanks for that recommendation.

The reason I'm on the market currently is that I was hoping to get something using my yearly 20% off REI coupon, and I had my eye especially on the REI Expedition (-20) or the Marmot Never Summer (0). I've heard good things about both, and though REI's website also sells a North Face 0 and North Face -20 bag, I haven't read or heard anything about those that suggest that they're worth the extra $100-$150 I'd be paying over the price of the REI or Marmot bag.

It's funny how subjective various peoples' perceptions of warmth are, as I've had a lot of people scoff at the idea of having a -20 bag even in 10-15 degree temperatures, but also a very trusted longtime hiking friend tell me she uses her -20 bag up to 40-45 degrees and is totally comfortable. Makes reaching an obvious decision frustrating

Really, though, I only ever expect to experience temps under, say, 10 degrees very, very rarely and it sounds like the 0 degree bag would cover me at least down that far, even sleeping as cold as I usually do. I like the idea of having the warmer bag precisely so I don't have to sleep with my down jacket on and heat up water for a Nalgene bottle before going to bed and all of that (worth carrying an extra 1-1.5 pounds to be able to leave the jacket at home and not have to burn through extra gas, in my opinion)...but maybe even without those aides the -20 would still be too hot to use in the 10-25 degree range?

I've owned quite a few bags by quite a few different manufacturers and in my opinion Marmot is the best of the big named brand bags. My feeling is that a 0 degree bag (Marmot Never Summer would be my choice of the ones you mentioned) is going to be plenty warm for all your adventures. On really cold nights you can always bring a hot water bottle to bed.

Get a 0 degree bag that is cut large enough on the inside that you can wear heavy clothing inside it. Do this, and a 0 degree bag can be pushed into the -20 degree range by wearing all your clothing.

I've got a Marmot Lithium 0 degree bag that I've used well below zero this way.

The Valandre Shocking Blue is designed for this, with an oversized torso cut so you can wear a big puffy belay parka inside the sleeping bag.

I've done a fair amount of mountains between 5,000-6,000m and a few between 7,000-8,000m, and many winter claimbs in the Sierra and I would go with a TRUE 0-degree bag. Something like a WM Kodiak. Although I used -40 on my 8,000m climb, the next one I'm bringing a zero. One of the guys went with a 30F bag and slept in his down suit. He froze his balls off but made the summit. The point is that you have a lot of clothes with you to use. The extra 2lbs make a drastic difference. Don't forget and effort it takes to stuff the -20 or -40 and bulk.

Everyone has made some great comments about this, but I figured I'd chime in with my 2 cents.

Firstly I agree with ExcitableBoy that of the big name brands Marmot is the best, as such I'd avoid TNF, MH or sierra designs etc.
When selecting a bag look at the down fill power and shell materials. You want the highest fill power (look for 750+) and a good light, but durable shell fabric. Your Sierra Designs sounds like its a 600 fill power which is pretty low grade these days, so get the highest you can afford. It'll mean a lighter, smaller bag for the same warmth.

As the_isalani mentioned a good laundering will help revive your bag, so try that first. Some dry cleaners specialize in this and it might be worth the $40 or whatever instead of doing it at home. If you do do it at home when you dry it, put tennis balls in the dryer with it to fluff up the down (it works).
Personally I feel that if you can afford it go for something like a Western Mountaineering, Feathered Friends or Valandre bag. I switched to Western Mountaineering and I would never go back. Marmot make some good bags like the lithium and plasma, but for the money go with a boutique brand.

A 0 degree bag should be perfect for what you're doing and as mentioned you can always throw on some more layers if needed. I know you say you want a warm bag so you don't have to, but 90% of the time you'll be hauling around another 1lb of bulk and sweating which fouls your bag. I feel like your better off carrying 2lbs of bag and 1lb of jacket than 3lbs of bag as the combo is much more versatile.

I have to disagree with Kia on going larger to accommodate more layers. I had a Mountain Hardware -20F bag that I bought large for this reason; it sucked, it was cold and I sold it. There was just too much dead space to heat up, it was inefficient and more bulk when packed. A little room for some light layers is fine, but any big layers will get compressed and/or compress your bag unless your bag is huge. It's probably different when doing an 8000m peak and sleeping in your expedition suit as Kevin said, but that's a whole different game.

the_isalani makes a great point that's often overlooked; your mats/pads. An inflatable paired with a closed cell will maximize your warmth and comfort.

Lastly another tip is to not only bring a hot Nalgene into your bag, but to drink something hot before bed and to eat something high in calories like chocolate and peanut butter. I have a few pieces of chocolate and a packet of almond butter with some tea before bed and it's awesome.

Victoriamatt wrote:Lastly another tip is to not only bring a hot Nalgene into your bag, but to drink something hot before bed and to eat something high in calories like chocolate and peanut butter. I have a few pieces of chocolate and a packet of almond butter with some tea before bed and it's awesome.

Great point! I was camping in Sequoia NP a few years back during an extreme cold snap. Not sure how cold it got, but it went well below the rating of my bag. I generally go for a lighter-weight bag and wear extra layers for extra warmth. On this particular trip, I was running low on food due to an accident with a leaky white gas canister contaminating a portion of my rations. I was getting miserably cold one night with my stomach growling very loudly. After a few hours of suffering without a wink of sleep, I decided to raid the bear can and munch some trail mix—only 1.5 ounces. It was unexpected and amazing! I was instantly warm and fell into a comfy deep sleep. It was like putting coal in a furnace.

There are a lot of good points here! Here are my two cents.

I sleep cold and need two pads under my torso.

I have a quiver of winter bags: 5F, -10F, and -20F.

I find that I only use the -20 Mont Bell Expedition Down Hugger in winter.

My winter trips are typically ski trips in the BWCA, where I cannot trust the temp forecasts and where the temps can easily get -20F.

I don't like pulling a sled throught the deep snow on the portages, so I go with the lightest pack possible. Currently, 20 pounds without food and water, but with kicker skins and the like.

The Mont-Bell bag weighs only 3.5 lbs in long, and I have never regretted bringing it.

I have gone with lighter bags, but don't like the scene where I need to wear all of my clothes, and anything else that I can stuff inside them, and then have to do push ups in my bag every hour to stay warm.

Don't be in a hurry to buy a bag just for the discount. The good ones, although quite pricey, will outlast you no matter how much you will use them.

@ year bump, what did you end up doing? Are you happy with your choice? I'm going through the same conundrum. Additionally, I want the versatility for possibly some big mountains in the future (denali Acon....). But I also would take this bag to CO, WA,OR ...etc for my alpine advertures in cold spring/winter. Thanks