Combined bag temperature rating

I'd like to get some opinions on this.

When you combine two bags (one inside the other) how much does the combined temperature rating go down?

For instance is a 30 dereee bag inside a 30 degree bag equivalent to a 0 degree?


Specifically, I have the GG lightweight bag that was discussed on this list a month or so back (50 degree rating, I think) .I also have an Eddie Bauer Bag liner (a poly blanket with zipper). Then there is the poncho liner I just bought (I slept comfortably with just it last night.-- low of around 60 degrees)

What temp could I be comfy at with combos of those three items??

I'm still playing with gear to optimize overall bulk for a given temperature.

When I win the lottery, I'll buy down and be done with it, but until then--- the dance goes on.

Miles of Smiles
Tom

Lot depends on how well they go together... if one restricts the other from full loft then you won't get a lot of gain...

First estimate take the send bag reating subtract it from 70, devide that number by two and then subtract it from the first bag rate for a combined value ex

Two 40 degre bags... 70-40 =30 devided by 2 =15 subtracted from other bag 40-15=25 for a first cut estimate of the combined bags... it may actually be better but probably not worse, so this works as a good conservative estimator, IMHO.

Pan

Thanks Pan,

That's just what I was looking for.

I have a weekend outing in North Florida coming up. With my 50 degree bag and a baag liner I should be good to 40, which is around the worst case low. I'll have the poncho liner in reserve.

Tom

Quote:

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Originally Posted by teblum

Thanks Pan,

That's just what I was looking for.

I have a weekend outing in North Florida coming up. With my 50 degree bag and a baag liner I should be good to 40, which is around the worst case low. I'll have the poncho liner in reserve.

Tom

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Where in North Florida?

We were going to go camp on the beach in the big bend area. Possibly as for north/ west as Destin.

My buddy came by today to tell me the trip is off. He has a conflict.

I hate it when they do that!!

Tom

Funny I was thinking earlier about what temp my 2 Guide Gear 50 degree bags would be rated together. I was guessing 30. It looks like it is closer to 40.

FF,

hey.. it may be good to 30... I just took a swag at a first cut estimating formula that, if off, would be off on the conservative side...

Pan

You might be right about that. I have used both bags with a low temp of 40. I was warm and felt I could have gone down further. Reason for using these bags insted of my Sniveler is my nephew was borrowing my Nest and my Sniveler was my underquilt.

The Guide Gear UL bag feels warmer faster than anything I've ever tried. (I'm a down virgin)

I wouldn't be suprised if two equaled near 30. A flannnel bag liner is supposed to be worth 10 degrees.

Tom

At around 1 lbs. 5 oz. each plus compression sack and around $20 (on sale)
it is pretty nice.

Quote:

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Originally Posted by teblum

We were going to go camp on the beach in the big bend area. Possibly as for north/ west as Destin.

My buddy came by today to tell me the trip is off. He has a conflict.

I hate it when they do that!!

Tom

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Sorry to hear that. It should be nice and cool here this weekend (in the low 40's) with the lowest temp (low 30's) expected Monday night. If you make it up this way let me know and maybe I could come by and meet you and check out your system.

FF, Et al,

If you are asking the rating estimate for top bag use in a hammock.... A normal full bag used as a quilt, with adequate insulation below you, will do better than its rating.......

Consider this... center of the shoulder to center of the shoulder you are 30-32 inches wide.... Your bottom wrap takes care of bottom and sides well passed center shoulder.... A regular bag opened is 62-66 inches wide.... you only need 4-5 inches to tuck in on each side.... therefore you have 52-56 inches of bag to cover 30-32 inches of you..... So you lay it loosely as to almost accordian the excess and you now have 150-200 % ore lofted bag abve you....better performance.


Note to all.... When cold folk start pulling the bag / quilt closed to eliminate any air space.... so far, so good.....HOWEVER, most end up snugging the bag/quilt too far, effectively reducing loft...not good...Think about it, there is a design requirement for a certain degree of looseness to allow the insulation to reach full loft, for max effectiveness.... the ground dwellers further exaccerbate the problem by moving around, changing positions and poking a knee, elbow, shoulder, foot etc into the tightly drawn material creating a thin spot .... then there is rapid cold invasion....( not unlike the hammock bottom/side issues.

There really are a lot of ways to incorrectly use a sleeping bag/quilt... Another is to continue using a 3/4 light weight summer pad and expect to be warm because you swithed to a 10-20 degree bag...cold feet and legs will defeat this plan....

Warm is as much a thinking game as anything.... When not comfortable the first thoughts should be where is the cold coming from, why, what can one do to eliminate the problem... then what can you do to add more capability/insulation.... for example if your feet are cold... and you already have on a warm pair if socks ... and you are using the summer pad as in the above example you will be better off putting extra socks or shirt/jacket under your feet than on them ( which BTW is often is a double wammyfor reduction of circulation, as well).

So in the end.... The real issue is what is the loft between the ears.

Pan

Nice post Pan. I feel confident about bottom insulation but often wonder how much I need on top.

Quote:

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Originally Posted by Peter_pan

So in the end.... The real issue is what is the loft between the ears.

Pan

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I think that is the best statement I have read on hammock forums yet.;)

Quote:

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Originally Posted by Peter_pan

So in the end.... The real issue is what is the loft between the ears.

Pan

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Should be no problem. Been a feather-brain all my life...

Quote:

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Originally Posted by Nightwalker

Should be no problem. Been a feather-brain all my life...

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Feathers are bad. you want at least 85-90% down....:p

does anyone know how companies rate sleeping bags?

are there standards for measurement or ratings, do they have machines or do they just put joe inside the bag and stick him in a freezer till he shivers?

seems like there's mixed standards, like I was reading about the panda bag/hammock I just ordered, it has 3 ratings, comfort, minimum and extreme plus a 5000mm water column rating... which I googled but didn't get much, seems like it's a pressure rating for water proofing, breathability or wind breakage or something... so many factors, i was watching man vs wild and he skinned the fur off some smelly dead deer and then cuddled his water bottle full of warm pee and everything... :p

so I have 3 questions if anyone knows, one is above

two is how did you come up with this formula?
three is how does water column factor in?

I don't know the answer to your questions but I've seen the 5000mm water thing on tags for columbia and northface jackets and ski pants that claim to be waterproof, windproof, and breathable. Next year's version will probably claim to enlarge your manhood too.

Is this a recommended way to increase warmth? I don't hear much about people doing this, but I have thought about it as an option.

Snull,
What I know, or think I know:
1) sleeping bag ratings standards - not really any industry standard. Some companies obviously rate conservatively and some do not. Some appear to rate by loft and some by other methods. Best way to use ratings is by checking boards such as this and ones for camping/backpacking to see what others think of a particular manufacturer's rating and then factor in your own factors (warm sleeper, cold sleeper, etc).

2) Some manufacturers will tell you how they rate and why they use the formula they use. Most do not tell you either. I imagine Pan came up with his formula above by a combination of experience and knowledge about insulation. His comments always seem to be pragmatic and founded in logic... which is much appreciated, especially considering he is also a manufacturer.

3) Water column - the number, usually in millimeters, is the height of a column of water that the material will not allow to pass through the material. So, a 5000mm water column rating means the material can keep a column of water that is 5000mm (is that 5 meters?) high from passing through it. These ratings are used to convey waterproofness, as the higher the #, the more waterproof the material is. However, perspiration is not water - it is water vapor and can pass through much smaller spaces than can water. So a highly waterproof material may still be breathable. Used to be, the more waterproof the material, the less breathable. Now things are starting to even out with some technical materials being both waterproof and breathable... and often expensive.

Hope this helps.

Quote:

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Originally Posted by Peter_pan

Lot depends on how well they go together... if one restricts the other from full loft then you won't get a lot of gain...

First estimate take the send bag reating subtract it from 70, devide that number by two and then subtract it from the first bag rate for a combined value ex

Two 40 degre bags... 70-40 =30 devided by 2 =15 subtracted from other bag 40-15=25 for a first cut estimate of the combined bags... it may actually be better but probably not worse, so this works as a good conservative estimator, IMHO.

Pan

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I found this in Articles; it's useful. However I had to read it 3 or 4 times to figure out what was being said because of the typos. I'm used to decoding ordinary posts, but I think articles could benefit from a little editing. It took me a while to recognize that "send" was "second". I think Pan's computer hiccuped and dropped two letters. The other misspelled words are easily recognizable. I think it should be clarified which bag is the first and which is the second. Which is inside the other, and why? If the bags have different ratings, you get different results if you change which one is "first" in the equation.
I'm guessing that with a rule of thumb like this there's much wisdom in Pan's caution in the first sentence.

Quote:

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Originally Posted by WV

I found this in Articles; it's useful. However I had to read it 3 or 4 times to figure out what was being said because of the typos. I'm used to decoding ordinary posts, but I think articles could benefit from a little editing. It took me a while to recognize that "send" was "second". I think Pan's computer hiccuped and dropped two letters. The other misspelled words are easily recognizable. I think it should be clarified which bag is the first and which is the second. Which is inside the other, and why? If the bags have different ratings, you get different results if you change which one is "first" in the equation.
I'm guessing that with a rule of thumb like this there's much wisdom in Pan's caution in the first sentence.

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As, mods,

This article was originally a reply to a post that was moved to the article section on general merit... My edit button capabilty does not reach back that far... Would one of you please edit this article... Thanks.

Pan

Quote:

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Originally Posted by Peter_pan

As, mods,

This article was originally a reply to a post that was moved to the article section on general merit... My edit button capabilty does not reach back that far... Would one of you please edit this article... Thanks.

Pan

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Mods,
I didn't see the thread this was taken from until I had composed my response to the article. The thread has lots of useful info, explained in more detail. It might be good to relabel the article's link to include "more info available" or somesuch, in addition to "discuss this article or suggest new entry".

When winter camping, I nest a down bag inside of a larger synthetic bag with very good results.

The outer syn bag actually works better in the combined arrgt when it does on its own.

inner - rated 15 deg F down bag - a true 15 deg F for me
outer - rated 15 deg F syn bag - but really only good to about 25-30 deg F for me because it is a wide cut with lots of dead air space

I have used the combined set down to -5 deg F and feel I still have a tiny bit margin.

I think the key is that the bags fit together extremely well so that the inner down bag gets full loft and there is very little dead air space between the bags and around me.

Of course, nutrition, hydration and fatigue play huge roles as well since it is the heat from my metabolism that heats the air trapped by the bags

I tried your formula, and it doesn't work for my experience.
So I though I should share :D

25+ years ago I lived in a tent through a couple of winters that had periods of extreme cold eg. -40

I was using two mummy/Dacron hollow fill bags that were rated to -7c
The bags were twins.

your formula would suggest:
-7c or 19.4 degree Fahrenheit
70 - 19.4 = 50.6F/2 = 25.3F
-19.4 - 25.3 = -5.9F

-5.9 degree Fahrenheit = -21.0555556 degree Celsius

So the combo of the two bags is good to -21c according to the formula.
I guess the question is to what degree of comfort is that -21c.

Here is my experience:
In my tent I slept in the two bags, on a single mattress off the ground.
I slept in boxer shorts and Tee shirt only . . .
(When it got colder I should have worn long johns. Duh.)
. . . Down to -34c/-29.2F I was just OK
-36c/-32.8F and I was not wanting to even wiggle my toes as they would feel the extreme cold of the bag.
-38c/-36.4F and I would spend 1/4 of the night, I guess closer to morn, shivering.
-40c/-40F I just happened to be far away from home, and in a motel room
- I was checking out a wood lot to horse log.
I never got a chance to do it, but that is where I was.

One thing is for sure, in the morning, minus the wind,
temp inside and out of the tent are equil. :scared:

More info: the tent had a 3/8" plywood floor on 2x6 joist,
one corner on the ground and the other three some what elevated,
it was built on a small slope.
The tent walls were a light industrial tarping, no insulation value.
The wood cook stove with oven, heated well enough to sponge bathe late in the evening.
Lighting was an old coal oil table lamp.
Shortly after bedding down the fire was out.
In the dead of winter the sun was down at 16:30,
and I would only spend an hour or two with supper and a night cap, journal entry if the pen worked.

I don't know if that helps, but it is just as it happened to me. :)

Quote:

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Originally Posted by tjm

When winter camping, I nest a down bag inside of a larger synthetic bag with very good results.

The outer syn bag actually works better in the combined arrgt when it does on its own.

inner - rated 15 deg F down bag - a true 15 deg F for me
outer - rated 15 deg F syn bag - but really only good to about 25-30 deg F for me because it is a wide cut with lots of dead air space

I have used the combined set down to -5 deg F and feel I still have a tiny bit margin.

I think the key is that the bags fit together extremely well so that the inner down bag gets full loft and there is very little dead air space between the bags and around me.

Of course, nutrition, hydration and fatigue play huge roles as well since it is the heat from my metabolism that heats the air trapped by the bags

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I'm on board with Tim

The difference in ratings from mfg are all over the board so the bottom line is the true loft of the insulation

Not allowing for varence in metabolisem the bottom line it all has to do with LOFT !!

The more loft = more insulation

Comprised insulation , less loft reduction in insulation= colder

The other factor is your pad or under insulation , its a third of your bag or more.

So when in a hammock the heat lose from below is a major factor.

When using two bags always make sure the over bag is larger then the inner
and insulation is not compressed.

A good wool sweater will add 5-10 degrees or more to a bag.

If you have cold feet its better to have a down foot sack that one can place both feet to gether then down booties.

To me there is down and there is every thing else !!

fourdog

I live in Kansas City Missouri, I have sleeped in a ENO hammock with no tarp and I only had a 20 degree sleeping bag and a sleeping bag liner or sheet plus a Fleece zip up blanket. I was hot and the outside was 18 degrees It could have gone down to 8 degrees and I would of been good as long as it don't rain. I plan on camping out tue with a Tarp and space blanket and sleeping bag and under that so hot rocks. I done this before and it was great. I was 12 inches above it (the hot rocks).The space blanket reflected the heat and with space sliding under the area it spread the heat. When I did this it was -10 outside and I was sleeping in long johns and sleeping bag and fleece blanket.

Quote:

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Originally Posted by bobcat13

Is this a recommended way to increase warmth? I don't hear much about people doing this, but I have thought about it as an option.

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I haven't tried it yet. Probably most helpful in deep winter condition and not shoulder season. I'd like to hear more how helpful this technique has been.

Geeking out here,

I decided I wanted to put Peter_Pan's formula into a shell script since my wife and I often find we combine bags/quilts in the winter.

It's a very basic script that requires bash and "bc"(basic calculator). Both are usually installed on most modern Unix variants. My Android phone doesn't seem to have "bc" installed:-(

This should run from the command line on most modern Unix based computers, Linux, MacOSX, BSD,... except Android and any other computer that doesn't come with "bc", unless you install it.

It will not work on Microsoft computers, unless Unix tools are installed.
Anyone want to write one that will run on MS Windows?

I call it "tempcalc"

Be sure to make it executable. Example:
chmod 755 tempcalc.



############################
#!/bin/sh

# tempcalc - estimates combined temp rating of two sleeping bag/quilts

# usage:
# tempcalc <bag#1> <bag#2>


totaltemp=`echo "$1 - ((70 - $2)/2)" | bc`

echo ""
echo ""
echo ""
echo "Temperature rating of item one = $1"
echo "Temperature rating of item two = $2"
echo "Combined Temperature rating = $totaltemp"
echo ""
#######################