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#132240 - 04/17/10 11:14 PM Sleeping Bag Actual Temperature
ratherBcamping Offline
newbie

Registered: 03/28/10
Posts: 4
Loc: New York, NY
Hey everyone, I have whats rated a 40 degree bag, what does that actually mean? I am thinking about going camping tomorrow night and it is expected to be 40 degrees at night. Should I be concerned that the bag doesn't actually keep you warm at that low of a temperature?


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#132243 - 04/17/10 11:31 PM Re: Sleeping Bag Actual Temperature [Re: ratherBcamping]
ChrisFol Offline
member

Registered: 07/23/09
Posts: 387
Loc: Denver, Colordo
Originally Posted By ratherBcamping
Hey everyone, I have whats rated a 40 degree bag, what does that actually mean? I am thinking about going camping tomorrow night and it is expected to be 40 degrees at night. Should I be concerned that the bag doesn't actually keep you warm at that low of a temperature?


If your bag is true to its rating, then depending on variable factors (kind of sleeper, wind, elevation, coverage, food intake, hydration etc) then you may sleep comfortably or it could get a little cool for you at night.

FWIW, if your bag is one of the higher-end models then you can expect it to be true to or even conservabtly rated. Lower-quality bags are, generally speaking, generously rated and could in fact be more like a +45/+50 degee bag.

In a brief and simple summary-- if I had a +40 degree bag and the temps were expected to hit +40 then I would bring some additional insulation.

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#132246 - 04/18/10 12:09 AM Re: Sleeping Bag Actual Temperature [Re: ratherBcamping]
Glenn Offline
member

Registered: 03/08/06
Posts: 2617
Loc: Ohio
As I recall, the temperature rating is supposed to indicate at the lowest temperature at which a bag will let you sleep "comfortably" under "normal" conditions (say, wearing minimal clothing, like shorts and a t-shirt, on a windless night in the open on a closed-cell foam sleeping pad. Or something like that.)

The problem in the US is that there are no hard and fast standards for "comfortable" or "normal", and each manufacturer gets to self-rate their bags. That leads to a system of "how low is that bag rated?" "How low are you looking for?"

There is a more scientific method used in Europe - it's designated by an EN rating, and bags from different makers with the same rating will pretty much keep you the same amount of warm.

So, absent an EN rating for your bag, it comes down to who made your bag. If it's Western Mountaineering or Feathered Friends, a 40 degree bag may still be warm at 35. Marmot will be pretty much dead on; Kelty, REI, and Campmor may also be pretty accurate, though I'd probably allow 5 degrees - call them a 45 degree bag. Off brands might very well mean a 40 degree bag is a 50 degree bag.

You can lower the temperature in which you can use a bag several ways. First, sleeping in a good tent will add perhaps 5 degrees to the rating. Wear long johns to bed, and you may get another 5 degrees. Now that 40 degree bag may let you sleep warm at 30. Add a pile or down jacket and pants, gloves, a balaclava, and maybe a stocking cap, and you may be able to get down near 20.

I say "may" because now two other factors come into play: bag size and sleeping pad. You want a bag to fit fairly snugly; if it's too loose, you end up with too much air to heat, and that 40 degree bag may only work like a 45 degree bag. However, if you're trying to push the limits of the bag by wearing a down or pile jacket and pants, you may end up being larger than the space inside the bag. If that happens, you end up compressing the bag's insulation against the outer shell, and lose warmth. (think Goldilocks: this bag's too loose, this bag's too tight, I need one that's just right.) The sleeping pad will not make a bag warmer; however, on very cold ground (say, in the winter or on snow) a pad that has too low an R rating will let the cold seep up from below and chill you, even though you have the right bag otherwise.

Really simple, huh?

Let us know your make and model of bag, and what pad you'll be using, and we might be able to give more specific advice.

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#132262 - 04/18/10 10:32 AM Re: Sleeping Bag Actual Temperature [Re: Glenn]
balzaccom Offline
member

Registered: 04/06/09
Posts: 2050
Loc: Napa, CA
And what kind of tent you'll be using. Some tents can increase temperature 10-15 degrees...which will let you get by with a much warmer bag in some areas.
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#132276 - 04/18/10 02:03 PM Re: Sleeping Bag Actual Temperature [Re: balzaccom]
Glenn Offline
member

Registered: 03/08/06
Posts: 2617
Loc: Ohio
Should've clarified that. When I used a "classic" nylon-walled inner and polyester fly (Eureka Timberline), I actually ran a test on night, hanging one thermometer inside and one outside. The temperature was consistently 10 degrees higher inside.

The last few years, my inner tent is 100% mesh (MSR Hubba or Carbon Reflex 1); the last test I ran only yielded a 5 degree difference.

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#132295 - 04/18/10 11:29 PM Re: Sleeping Bag Actual Temperature [Re: Glenn]
balzaccom Offline
member

Registered: 04/06/09
Posts: 2050
Loc: Napa, CA
Yep. We have two tents. One is a heavy double walled Eureka that does really keep us warmer. the other is my homemade single wall that is really light...and breezy!
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#132303 - 04/19/10 01:32 AM Re: Sleeping Bag Actual Temperature [Re: balzaccom]
OregonMouse Online   content
member

Registered: 02/03/06
Posts: 6745
Loc: Gateway to Columbia Gorge
Here's a place to find out about the EU's EN13537 ratings for sleeping bags. Go down a ways to "how to understand...."

Most American companies don't even use them; you could check their .uk sites but I wouldn't be surprised if some make different bags for the European market. For those that do use the EN ratings (REI is one), they often give only one rating--note that there are three. I strongly suspect that the one EN rating shown may be the "survival" rating--the one at which, if you're lucky, you won't die of hypothermia before morning. Just for fun, I asked a clerk at REI Friday which EN 13537 rating their bags used and he didn't have any idea what I was talking about! It has been noted that different European labs have produced different ratings for the same bag, so even their system is not all that accurate. But these ratings are certainly a lot more objective than the completely fictional ratings that many US companies use. But if you see an EN rating advertised, find out which rating it is before you trust it! Personally, I'd want the comfort rating for women plus 5 degrees F, but I am, admittedly, a COLD sleeper!

From my own experience and discussion with others, Western Mountaineering, Feathered Friends and Nunatak have accurate if not conservative ratings even though they don't use the EN standard. Marmot and Montbell high-end bags are (by several accounts including mine) about 5* off, and by accounts from warmer sleepers are just right. None of these are cheap! Of course the European bags sold in this country (most of them extremely expensive) should show all three EN13537 ratings on their label or at least their website. If they don't, be very suspicious!


Edited by OregonMouse (04/19/10 01:35 AM)
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#132306 - 04/19/10 02:15 AM Re: Sleeping Bag Actual Temperature [Re: ratherBcamping]
lori Offline
member

Registered: 01/22/08
Posts: 2801
This is precisely why I never go backpacking with new gear - sometimes, it doesn't perform as labeled. If you are car camping it's a perfect opportunity to see if your particular bag works as advertised.

If you spent more than a hundred bucks on it, and did not buy it at Walmart, Sport Authority, or Target, you increased the chances of it being warm enough for you a great deal. smile

I have backpacking quilts that I trust to their maker's estimated ratings, but only because I have used them myself to those temps. Even with an EN rated bag, you don't always find that the listed temp is accurate FOR YOU - this is such a subjective thing that it's best to give it a good test. Eat well before bed, stay hydrated, wear a base layer or similar that you are comfortable sleeping in, put on some clean sleeping socks (keeps your bag cleaner inside), shake out or give the bag some time to loft up after you set up camp, and get yourself a good sleeping pad to keep you warm underneath - the bag bottom compresses under you and does little to warm you. For temps above freezing something like a single CCF pad (cheap and bulky) or self inflating Thermarest will do nicely.

Lastly, you will want to practice good site selection for your shelter. Camping in a canyon bottom, near water, will be colder than camping partway up a ridge - cold sinks. Camping at the top of a ridge will subject your shelter to the brunt of any wind that exists and resulting wind chill. Everyone likes to camp near water, and tent users tend to set up in the same spots - look at spots that are obviously overused before using them again, some folks end up with a pool of water inside the tent if it rains because they put it in a depression where water collects. It matters not at all whether you have down or synthetic, a wet sleeping bag is miserable and cold.
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#132370 - 04/20/10 01:40 AM Re: Sleeping Bag Actual Temperature [Re: lori]
OregonMouse Online   content
member

Registered: 02/03/06
Posts: 6745
Loc: Gateway to Columbia Gorge
You're so right, Lori, a dummy with thermometers attached is definitely not the same as a living, breathing person! Each of us is different!
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey

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