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I am looking to buy an ultralight sleeping bag, that would be warm enough for sleeping in the Alps in summer comfortably. I would be sleeping in a tent on a sleeping mat. I would probably be staying at around 2000, max 2500 meters. And I would expect I could be out there in between June and September. According to my research on the Internet, the lowest temperatures at that time and altitude should be around 0°C, possibly a couple degrees below, but most likelly a bit above. How warm do I need the sleeping bag to be?

Actually, I believe my question can be subdivided in the following subquestions:

  • Can I safelly assume, that it will not get much below 0°C in summer in the Alps at around 2000 meters altitude?
  • How much warmer will it be inside a tent? (very small two-person tent, two layers, no heaters)
  • Sleeping bags have temperature ratings for three categories: comfort, limit and extreem. Should I look at the lowest value of "comfort" temperature if I want to be able to sleep without feeling cold?

UPDATE:

So I have bought a sleeping bag, and would like to update the question with my experience.

I have decided to go with the ultralight (and expensive) option in the end. My new sleeping bag is rated +4°C comfort, and -1°C limit. I have tested it on a few trips in the mountains during this summer. When sleeping on warm summer nights at altitudes around 1500m, it was actually too warm. No surprise there, and not a problem either.

Another trip I took was in the end of September, when the nights were fairly cold already. I am not sure about the exact temperature, but it must have been in between 0 and 5°C. I was sleeping at around 2400. I must admit, I was a bit worried, but the only time I was cold was while cooking dinner outside of the tent. The sleeping bag combined with a cotton sleeping bag liner was certainly enough.

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    A lot will depend on you. I will need a winter/-20C sleeping bag in any but the hottest weather. In a test I saw that one of their test team slept comfortable in a summer only sleeping bag in very cold weather, only you can know what kind of temperatures you need to sleep.
    – Willeke ♦
    Jun 20 '18 at 17:21
  • I think I am none of the extremes with regards to resistance to cold while sleeping. Let's assume I am an average person. The problem is that I am always too optimistic when estimating my capabilities, so that's why the question on the Internet. (:
    – april rain
    Jun 21 '18 at 7:48
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Warnings and Caveats

Everyone sleeps different. Some people sleep much warmer than others while others sleep incredibly cold. You can try and determine this in your house or better your backyard, but you really won't know until you are sleeping while hungry, exhausted and in the actual weather you are dealing with. Humidity effects people differently and so does altitude. The temperatures you have experience most recently also affect how you sleep. Just because you are a warm sleeper at -10 does not mean you will be a warm sleeper at +10.

To be ultralight in a critical piece of gear like a sleeping bag means to know your body. There is nothing stopping you from buying an ultralight sleeping bag, but if you don't know how you sleep, you need to buy an ultralight bag with warmth to spare.

Next, while I always want to be safe, I also want to be usually comfortable. Some areas have very consistent temperatures and the very rare incredibly cold night. In these areas I plan on being comfortable most nights and figuring out how to survive the once a season cold night (e.g., is it an area I can hike to lower elevation or the safety of town or can I do jumping jacks all night long). Other areas every night is essentially the coldest it gets. For these areas I never want to get close to the safety limit since I will never be comfortable. I would describe the Alps as being pretty consistent in temperature in the summer meaning you should expect to actually experience the extreme low on a regular basis.

Can I safelly assume, that it will not get much below 0°C in summer in the Alps at around 2000 meters altitude?

The Alps are a big region, but that seems like a reasonable lower limit of expected temperatures. If I had did not have an escape plan, I would want to make sure my system would allow me to be safe, but slightly unconformable at that temperature. Lacking an escape plan, beyond get up and hike, I would probably want to sleep with all my cloths on and in a tent down to -10C. If I can check the weather and choose days and campsites, and don't mind canceling a trip because it is cold, 0C is probably fine as a low limit of sleeping safely.

How much warmer will it be inside a tent? (very small two-person tent, two layers, no heaters)

This depends on a number of factors (wind, tent, number of people, sleeping bags, etc. This blog post claims 20 degrees F, but I wouldn't count on that much of an improvement. It is also worth noting that sleeping bag ratings assume a pretty optimal tent.

Sleeping bags have temperature ratings for three categories: comfort, limit and extreem. Should I look at the lowest value of "comfort" temperature if I want to be able to sleep without feeling cold?

The EN 13537 standard has a lot of values. The extreme temperature is essentially the lowest temperature that an average women can survive. This is a very cold night. Even though women sleep colder than men, this is still a very cold night for a man.

The Limit temperature applies to a man sleeping curled up and not feeling cold. This is by no means a comfortable night, but generally is far away from risks for the average man. If I was an average man and didn't have any thing but a light set of cloths, a tent, and a good sleeping pad, and had an escape plan, I would probably want the limit temperature to be around 0C. With a light weight puffy jacket, I might be willing to go warmer depending on how often cold nights happen.

The Comfort temperature is for the average woman sleeping in a relaxed position and feeling comfortable. For an average man who is willing to curl up and has a light puffy jacket, this is probably too warm.

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  • Thanks for the detailed answer with all sorts of considerations. I did not realize sleeping bag ratings assume you will be using a tent.
    – april rain
    Jun 25 '18 at 8:00
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1) You can expect the lowest Jun-Sep temperatures will be above 0 °C most of the time.

Coldest temperatures on Kredarica (2515 m, in Slovenian Alps) in 2016:

  • Jun: -1 °C
  • July: -2.1 °C
  • August: -3 °C
  • September: -2.9 °C

10-day forecast for Kredarica: The lowest morning temperatures between 21st and 29th June will be from -3 to +8 °C and this is colder than usually.

2) You can be much warmer in a tent, because it prevents against wind, which can be strong in Alps at times. It also prevents against moisture (dew).

3) For these temperatures, I would buy a sleeping bag -5 °C Comfort. You can find such a bag that weighs about 1.5 kg. Speaking from experience. Temperature ratings on sleeping bags can be overrated by more than 5 °C.

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    With an ultralight mindset, recommending a bag with a comfort rating 2 degrees lower than the expected most extreme condition seems overkill. As a bag with a 0 C comfort rating probably has a -25 degree extreme (you probably will not die or lose any limbs), it seems more reasonable to look at average temperatures and go with a comfort rating closer to that.
    – StrongBad
    Jun 20 '18 at 17:55
  • yes, I agree, this is a way too heavy and warm sleeping bag for me. I am looking for something half that weight. Yes, I know I will have to pay the price, but I am ready for it, because I plan to make a heavy use of it in the near future. Mostly when traveling, but it has to be fine to be used in the mountains as well.
    – april rain
    Jun 21 '18 at 7:52
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    My experience is that if I sleep at 0 °C in a sleeping bag with 0 °C Comfort, I will never be comfort even if I'm fully dressed. But I was never buying very expensive bags. Also, the "limit" temperature is useless for me and "extreme" is meaningless. Because, when I sleep, I want to sleep, not just survive.
    – Jan
    Jun 21 '18 at 10:43
  • Fully dressed can be colder.
    – paparazzo
    Jun 23 '18 at 16:11
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Can I safelly assume, that it will not get much below 0°C in summer in the Alps at around 2000 meters altitude?

I would say that very broadly this assumption will hold, but the question is what you will be betting on it. There can certainly be situations where it gets colder, although this is probably quite unlikely.

If it getting colder means that you would be uncomfortable for a single night, or be forced to maybe wear all your clothes inside the sleeping bag that is suboptimal but (in my eyes) a small risk. However, plan to bring very limited/light-weight gear and plan spending a longer time in exposed/difficult terrain then the risk will be a different beast altogether. We would have to know more about the exact trip that you are planning.

How much warmer will it be inside a tent? (standard, small, no heaters)

This of course depends on the tent, how exposed you will pitch it, the prevailing weather/wind and also it's occupants. My experience is that a full 3-person double-wall tent will easily be heated to a couple of degrees warmer than the outside temperature. How big the difference will be is however hard to predict.

Sleeping bags have temperature ratings for three categories: comfort, limit and extreem. Should I look at the lowest value of "comfort" temperature if I want to be able to sleep without feeling cold?

This varies a lot depending on the manufacturer of the sleeping bag. After all what does 'extreme' mean exactly? That you'll survive but with both arms and legs frozen off? Manufacturers will always try to come up with the most exiting numbers to sell their products, so don't put too much faith in them.

My suggestion here is to go to your trusted local outdoors store and talk to them about the sleeping bags they have. They should be able to recommend one that fits your needs. The shop in my home town for example does their own sleeping bag grading, allowing you to compare sleeping bags of different manufacturers.

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Ultralight and to sleep without feeling cold are inconsistent.

Ultralight mean to be as light as possible with sacrificing comfort.

If you want to be comfortable then go with the comfort rating.

Tent is not much warmer. It protects you from wind, rain, and snow. The rating is basically based on being in a tent.

On colder weather you can extend the bag with a vapor barrier liner.

I know bags are expensive but if you want a travel bag and a mountain bag consider two bags.

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  • I think you mean without sacrificing safety and not comfort. Even if you are not trying to cut every possible gram, a 0 degree ultralight bag (high fill down, thin shell, light zippers), will still save a bit of weight over a 0 degree non-ultralight bag without sacrificing much/any comfort. The weight savings come from increased cost and decreased durability.
    – StrongBad
    Jun 23 '18 at 16:44
  • @StrongBad Don't want to go there. I mean sacrifice comfort. When you sacrifice comfort you do sacrifice safety. I will sleep cold at 0 means if a rare storm hits and it is -20 you have possibly sacrificed safety. Pack minimum calories means if you get stranded you could sacrifice safety. A bag can be ultralight but decision on -20, 0, 20 is what I am referring to. OP does refer to comfort so to me it is about ultralight as a practice.
    – paparazzo
    Jun 23 '18 at 17:14
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    Not my downvote, but I feel like your first two sentences contradict each other. If ultralight means your are cold when you sleep, doesn't that mean you sacrificed comfort?
    – StrongBad
    Jun 23 '18 at 17:53
  • @StrongBad I feel like my words are clear. inconsistent
    – paparazzo
    Jun 23 '18 at 21:10
  • Yes, two bags would be ideal. To be honest, I already have a really warm but heavy and bulky sleeping bag for those cold nights in the mountains or for up north. And a smaller simplier one for indoors or warm summer nights in low altirtudes. But I am going on a very long trip, which will include sleeping in all sorts of conditions, some of which will resamble camping in the Alps. I will have to carry all my weight on the shoulders, so sleeping bag being light is really essential. And while I still live in the Alps, I would like to make a few light-weight trips through the mountains as well.
    – april rain
    Jun 25 '18 at 7:51

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