How does the temperature rating of a sleeping bag work ?

Ausseknifeknut

Ausseknifeknut

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if a sleeping bag is rated to minus 5 degrees , does that mean it'll keep you warm up to the point Of it being minus 5 degrees outside ? And what does the plus 5 degrees rating mean ?
 
It can only trap the heat that you generate.

People differ in how much heat they generate.

You may be more or less healthy, fed, hydrated, and warm when you enter the bag.

The ratings place the insulation value of the bag in relation to other bags.

All this means that the rating is only an approximate value for you in particular at a given moment and situation.

A nice way to see if it works to -5 for you is to try it out at -5 in your back yard.
 
Good article

But you have to know how you sleep, hot or cold

I sleep hot and can do sub zero in a three season bag and a parka
I know women that need a four season bag for the Fall

What sleeping pad

Then there are tricks
hot chocolate drink or a candy bar before sleep
A water bottle with hot water in it
 
When I worked at REI, I explained that if you want to be toasty warm at -5 degrees F don't get a -5 bag get a -20 degree bag. Also the condition of the insulation matters because synthetic insulation loses loft over time thus losing insulation ability.

Also the trick, add clothes if you need a warmer sleeping system, to stretch a bags limits.

An insulating ground layer is important too, ratings go out the window if you sleep on bare ground.
 
The loft of polyester insulation last much longer is:

1. You let the bag air dry (dryer heat can take the "permanent wave" out of the insulation); and
2. The bag is stored in an uncompressed state.
 
also depends on the company, the ones that give an EN 13537 should have three numbers, Comfort, transition (where you will be chilly) and extreme (you will be cold, but should be able to avoid hypothermia....should) The ones that don't especially australian companies (blackwolf, roman, oztrail and the like) the ratings tend to be "survival" or I guess some kind of minimun. I sleep cold, but I have a oztrail bag that is rated to 5C, realistically its good for about....25C. Granted its a cheapo, so not much to be expected, but gives you an idea of how they think about "rating" their bags. I also have a katmandu down bag that is comfort rated to 11C, transition to 6C on the EN scale, I'd say that its about right, with it all zipped up and wearing thermals, 10 degrees has been alright (not warm, but not chilled either) in it. I figure that for me, the thermals work it out to closer to the average joe. The ratings also don't factor for humidity, or wind, so keep those in mind as well.
Lastly personal conditioning make a difference. If you are used to 35C all day and working hard, on a cool night you'll need a warmer bag than if you are more comfortable sitting still on a 15C day. That's harder to judge, I'd say add a few degrees into your planning if the daily temp swing is very high (desert and the like)

Clothes can create diminishing returns, as tension on the skin makes you feel cooler than you are, or can cause additional compression on the insulation. as can things like the hot water bottle or handwarmers. it better to go to bed cool and warm up, than hot and cool off, at least that's what I've found.
 
billym said:
When I worked at REI, I explained that if you want to be toasty warm at -5 degrees F don't get a -5 bag get a -20 degree bag. Also the condition of the insulation matters because synthetic insulation loses loft over time thus losing insulation ability.
Click to expand...

That is pretty much the way I view the ratings.
 
Layers piled on top of your bag can also, in Brother gadgetgeek term, create "diminishing returns" as the weight of those layers crushes the air out of the inner layers.

Over a series of nights, down insulation absorbs moisture that constantly escapes from your body and, thus, loses loft.

The same moisture can condense, even form ice, to the outside of a polyester-insulated bag and force out air, reducing loft.

Ratings are only guidance. Situations alter cases. A margin for error sounds real good, even when conditions allow you to try to dry out the bag in the field between uses.
 
billym said:
An insulating ground layer is important too, ratings go out the window if you sleep on bare ground.
Click to expand...

As has been said a good insulation ground barrier can add as much as 5 degrees. And so can an effective wind block/barrier add about another 5 degrees. I've sleep down below my bag's advertised rating by using a reflective reusable space blanket and pad under me and in a tarp shelter or in a bivy sack as my wind barrier.
 
Good insulation under you helps a ton. So does getting out of the wind. I like to bring a bag that's rated to a lower temp then where I'll be sleeping. Some nights I sleep warmer and some I sleep cooler. The extra insulation helps me stay warm regardless of how I'll be that night. :)
 
Colin Fletcher's The Complete Walker is a great source on hiking and camping in general. With a good ground pad and appropriate sleeping bag (I've used two in -40 conditions) you can stay warm in practically any temperature. Synthetic insulation works great as it does not absorb moisture like down. Wearing clothes inside your bag can decrease the insulation rating as cotton in particular absorbs moisture. Polarfleece/microfber fabrics don't hold moisture and are better for sleeping.
 
Fletcher writes very well. Probably the best quality of prose in the field. Several books.

His information is, in some respects, decades or generations, old. (His search fior a decent small flashlight seems poignant given what we have available.) Still, well worth reading.

The "new" editions have only cosmetic changes. Mostly verbatim the same.
 
One of the advantages of older info is it helps put things into perspective. Yes the old books all talk about the limits of down, but now with modern treatments and fabrics that is largely mitigated. However, the thought process should still be there for gear selection because often what was once high dollar gear is now available much cheaper, and by knowing what you are looking for overall, you can select gear without the marketing playing a part. For example we are rapidly approaching a time when LEDs will be more efficient per weight than candles, but without knowing why certain things were recommended back in the day, it would be hard to understand why change is better. (everything is better than a carbon zinc battery these days)

Also keeping in mind that a lot of the old writers used bags or blankets with a canvas cover, as a fire was a foregone conclusion, or may have felt that spending the cold part of the night awake was part of the joy of the woods. For me, if I'm camping out for work, those hours of sleep are needed, so I can't afford to get my 8 over the course of 14, and I'm not going to be carrying canvas, so fire-warmth is a non-starter as well.

Anyway, one other factor that leads into the sleeping hot or cold is metabolism and calorie intake. Some guys have fuel to burn all night, I'm more like a twig-stove, gotta keep fed or the fire is going out. so for me there is a bit of a balancing act, not going to sleep too hot, as I find that then as I fall asleep the temp regulation is a bit off, and I'm in "cooling down" mode, but not so cold that I burn off all my spare energy four hours in. Oddly, that means I can get colder from hotter days as I tend to eat less when its hot out, and stuff my face when its chilly. It also plays into your planning as far as food consumption and emergency planning, a light sleeping bag that keeps you warm in perfect conditions, and well fed might not be enough on a night when the rations run out. Not a problem for some guys, huge problem for me.
 
Not sure what the official answer is, but I've found that this varies by brand and quality. My snugpak has 2 numbers on it, the comfort rating, and the low rating, that being said I typically add 15-20 degrees to those numbers for my personal level of accuracy and comfort without adding a liner.
 
Thickness of bag for average, well person inside a tent per U.S. Army some years ago
Low Temp Tot. Loft of bag

40f 3.0"

30f 3.5"

20f 4.0" Shake out your bag to fluff it up, and lay it on the
floor. Wait ten minutes and measure total loft.
10f 4.5"

0f 5.0"

-10f 5.5"

-20f 6.0"

Sleeping Bag Temperature Ratings: Fact or Fantasy?

The E13537 Dummy

Introduction

The European Sleeping Bag Temperature Rating Standard (EN13537) was supposed to be a great thing for outdoor manufacturers, retailers, and consumers. Finally, we’d be able to compare sleeping bag temperature ratings in a reliable and objective manner.

Ah, I have some bad news. I was browsing the Outdoor Industry Association’s web site last week and came across a June 2009 report that shows that the EN13537 standard is potentially misleading. I was shocked to come across this paper, so I contacted it’s author, Dr. Elizabeth McCullough, a noted textile scientist at the Kansas State University, and she explained the problems with the testing procedures to me in more detail.

Everyone’s Manikin is Different

But before I dive into those, it’s useful to understand how the temperature rating test is performed. REI has a good explanation of the EN 13537 standard in the experts tips section of their web site. Quoting them, “For EN 13537 temperature tests, a full-size mannequin with heaters and temperature sensors is dressed in one layer of long underwear and a hat. It is placed inside the sleeping bag being tested. The bag is laid atop an insulating sleeping pad inside a climate-controlled chamber. The mannequin is heated to simulate body warmth and measurements are taken of the air in the climate chamber and the “skin” surface of the mannequin. From these measurements, the insulation value of the sleeping bag is calculated.”

Currently, there are 5 different testing centers around the world that test sleeping bag temperature ratings using this setup, including Dr. McCullough’s labs at KSU. The problem, says Dr. McCullough is that every lab’s manikin is different and that there is no common definition of the thermal properties of the tracksuits, socks, hat (really a face mask), and sleeping pads, used in the test process.

Consequently, the results of the different centers may vary significantly, and while the test itself is scientifically sound, she’s been advocating for a consistent definition of these non-standard testing variables. As it stands, inter-lab variability is unknown, making it impossible to compare temperature ratings from the different centers.

Sadly, this has not happened. As it stands, the European standards group responsible for the temperature rating standard is not allowing the Outdoor Industry Association (OIG) to attend the group’s standards meetings. Dr. McCullough has advocated the creation of a consensus document from the OIG to the EN standards body protesting the current test definition, but progress along these lines has been slow. Dead slow.

Who Can You Trust?

Adoption of EN13537 is now widespread in Europe, and several American sleeping bag manufacturers including REI and Marmot have started labeling their retail sleeping bags with it.

Unfortunately, Dr. McCullough advised me that highly insulated sleeping bags could vary as much as 20 degrees (F) in their ratings and that there are no common test procedures defined for non-mummy bags. In addition, other researchers have documented additional problems with the test procedures (see papers linked below).

Where does that leave consumers and why haven’t sleeping bag manufacturers that have adopted EN 13537 been more forthcoming about these issues?

Background Publications

http://www.outdoorindustry.org/pdf/EN13537Mccullough062209.pdf

http://www.outdoorindustry.org/pdf/EN13537TestLabComparisonMethod.pdf
Click to expand...
 
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