A Major Newbie Question About Sleeping Bags

[EarlyStarter]

I feel incredibly stupid asking this because it seems to be common knowledge but what exactly are the sleeping bag ratings? What do they stand for?

[cupid]

20* means you should be warm inside of the bag if the temperature outside of the bag is 20* or more.

[SGT Rock]

Just know that it is a manufacturer rating. Not all are created alike. So if say Western Mountaineering rates their bags at 20F, they mean it and probably with a good margin. But if you are buying Slumberjack their 20F is probably more like 30F.

[skinewmexico]

With a lot of manufacturers (not WM), a 20 degree rating means you will survive a night at 20 degrees, but not necessarily enjoy it.

[Hoop]

Western Mountaineering (others also, maybe) has good info on their website about fill, ratings, proper size, etc.

[Kirby]

It means that if its 20 degrees out and your in a 20 degree bag, you can rest assured knowing you'll wake up the following morning.

Chances are you will not have slept well.

[SGT Rock]

European bags are rated at like three temps if I remember right - best use, comfortable, and lowest.

[Blissful]

And the ratings varies like the wind...

Which makes reviews and opinions pretty important to know if they are accurate.

[Billygoatbritt]

depends on your internal furnace. some stay toasty in a 20* bag and others freeze.

[Marta]

Ray Jardine suggests using a simple measurement: Lay the bag or quilt on a flat surface and measure how much loft it has with a ruler. Our zero degree bags both have about 6" of loft. That includes the upper and lower layers, though, so you might say that 3" of thickness will keep you warmish at zero degrees.

How any sleeping bag achieves its loft depends on the quality of the filler material. Really good goose down can loft up three inches and not weigh much at all. A coarse synthetic will weigh many times more to get that same thickness. Sleeping bag filler is like women's underwear: smaller and lighter = more expensive

Besides the filler material, other things that affect a sleeping bag's temperature rating are the thickness of the baffles (which allows the filler material to loft up without compressing it), and whether there are thin spots that will leak lots of air, or whether it is more laboriously constructed to prevent cold spots (hoods, draft collars, zipper insulation, etc.).

There are various claims for miracle fabrics and substances that are warm without being thick. I'm suspicious of that. Somehow they never work quite as well as advertised.

[skinewmexico]

Everything you want to know about European sleeping bag standards and testing. http://marmot.com/fall_2008/equipmen...info/certified

[Jayboflavin04]

Just know that it is a manufacturer rating. Not all are created alike. So if say Western Mountaineering rates their bags at 20F, they mean it and probably with a good margin. But if you are buying Slumberjack their 20F is probably more like 30F.

I will "agree" 100% to this statement concerning slumberjack bags. I had a 20 degree bag that I was comfortable in at 35 degrees with clothing under a tarp. I got couple cold drafts throughout the night (not a big deal). I could have gone colder but I feel like I was starting to push the good nights sleep boundry. I sold them both to someone on this site. He had them out last month on the AT. He said they were wonderful. So it also depends if you are a warm or cold sleeper.

I am totally ready to try out my Western Mountaineering Ultralight in a couple weeks!!!
Would be nice to see some low 30s to give a go.

[Franco]

The European rating is a very good starting point. Once you know that a 32f rated (comfort standard) bag is too cold for you at that temperature , than look for one that is rated 28f ( or whatever)
but you do need a starting point.
I used the beer analogy before. Once you know that after 5 beers you love everybody, the next time you drink a beer with the same alcohol content, stop at 4.
In my case 3 is plenty.
Franco

[maxNcathy]

I like a 15 degee difference..If it is 30F in my tent I like to have a sleeping bag rated to 15F..unless I wear alot of clothing to bed which I don't prefer to do usually.
I am referring to very good quality down sleeping bags.

[Tipi Walter]

depends on your internal furnace. some stay toasty in a 20* bag and others freeze.

This is very true and changes periodically due to age, physical shape, exhaustion, etc. My rule of thumb is 15 degrees: if a bag says it is rated to 15F, plan on it working to about 30F. This doesn't hold true with some brands like WM or Feathered Friends, though. I have a WM Puma rated to minus 10F and it works well(for me)down to around -5F. Closer than most. I had a Marmot zero bag(Couloir)that stopped working at around 10-15F, so I got the Puma.

[theinfamousj]

I use sleeping bag ratings to give a sense of scale to a manufacturer's bag line. Since I am a cold, cold sleeper, I know that I need the warmest bag that the manufacturer makes in order to go winter camping. So I won't take the 20*F bag or the 0*F bag, but I will take the -5*F bag. Will the -5*F bag keep me toasty at -5*F? Who knows. But I do know that it is a manufacturer's warmest bag.

For a three season bag, I know that I need something in the middle of a manufacturer's range, again because I'm a freezing cold sleeper.

Using them to compare across manufacturers? That would require each one to use the same standards. Currently, this only happens in Europe.

[stranger]

Just keep in mind that a sleeping bag rating is not nearly as important as the following:
- gender
- ground insulation
- your metabolism (spelling ???)
- wearing a hat
- blood circulation
- full or empty stomach
- wind
- stomach or back sleeper
- hydration

Remember you can vent a sleeping bag, but if you are cold you are going to have a long night.

[shelterbuilder]

I use sleeping bag ratings to give a sense of scale to a manufacturer's bag line. Since I am a cold, cold sleeper, I know that I need the warmest bag that the manufacturer makes in order to go winter camping. So I won't take the 20*F bag or the 0*F bag, but I will take the -5*F bag. Will the -5*F bag keep me toasty at -5*F? Who knows. But I do know that it is a manufacturer's warmest bag.

For a three season bag, I know that I need something in the middle of a manufacturer's range, again because I'm a freezing cold sleeper.

Using them to compare across manufacturers? That would require each one to use the same standards. Currently, this only happens in Europe.

This illustrates the crux of the whole ratings issue. Ratings are only useful in comparing 2 bags from the same manufacturer, since there is NO industry standard for ratings. But you have to know if YOU are a warm or a cold sleeper before the ratings will have any practical use for you. As a newbie, if you buy a bag that's rated for 20* and use it in the Fall on some nights when the temperature falls to, say, freezing, and you get cold, then either you're a cold sleeper, or the company's rating system is a bit skewed in the company's favor.

Personally, I'd rather err on the side of warmth - if I'm shivering all night in a cold bag, I won't have a good trip. YMMV.

[JAK]

I feel incredibly stupid asking this because it seems to be common knowledge but what exactly are the sleeping bag ratings? What do they stand for?

Mark Verber does a good job explaining some things.
http://www.verber.com/mark/outdoors/...ep-system.html

There are differences between people, that requires more loft for some than others, but I don't think its in the amount of BTUs we produce for our surface area. There may be some minor difference there but I think the biggest differences between people is in the skin temperatures that they can tolerate. Some people seem to insist on sweating in their bags. Others can tolerate average skin temperatures 5 or 10 degrees below the skin temperature required to stop excessive sweating, which is 85F. For the record, I think there are variations due to BTU output, but bigger variations in loft requirement due to skin temperature tolerance. Methods people use matter also, and that is most critical in winter. People need special skills for 20F, and additional skills for 0F, and so on. Some extra loft helps make up for missing skills, but only go so far.

Personally I think the Army loft recommendations are the most objective, perhaps at the expense of comfort sometimes, but not safety. The Western Mountaineering folks, and others, make the best bags, but tend to have more of an interest in creating bags much bigger and more expensive than people actually need. It is better to understand loft, and how much is actually needed, and why, and to develop your own experience and guidelines using loft rather than bag ratings. Of course to do that you still need to buy a bag. For that purpose, first look at bags that fit you length and girth, then compare bags bases on things like down quality and ounces of fill, which is more objective than manufacturers own bag ratings, and loft claims.

I would suggest the Army loft recommendations ratings are for average skin temperatures of 85F, cool enough for the skin to vasoconstrict a little and stop excessive sweating. If you use those loft recommendations you will still be comfortable. For temperatures below 0F it starts to get difficult to breath, so you need to learn to use a scarf or balaclava, and there are other considerations like getting into and out of you bag. There is a good case for an extra inch of loft below 0F, to give you a little extra to make up for transient effects, like having to warm up a cold body after its been exposed. Above 0F this isn't so critical, and is often better accomplished by getting the body out and dressed and active. The Western Mountaineering ratings are conservative. Personally, I would rather put that extra weight into clothing. In general though, I would use loft, not bag rating, but I always suggest people do there own tests, and develop their own methods and guidelines.

[JAK]

Surface area is an interesting consideration. In theory, if the inside of your bag is 12% longer in length and 25% wider in girth than it needs to be, it would need to be 45% greater in loft to make up for it. That can be the difference between -20F and -40F, but also one size up, so in theory 80% heavier! In practive however, some of that extra surface area disappears around you. You need a little extra space, but not much. If you want to use that extra space for clothing when the temperature is below your bags loft, that's space well used. If you want to use that extra space for storing your boots, that's not a bad practice, but your bag may need to be a little bigger, and loftier, and heavier. The idea of a sleeping bag is to insulate the minimal surface area, plus a little.