Doubling Up Sleeping Bags

[mts4602]

I'm going on the AT in the Smokies next weekend and the temps on Mt. Leconte have been down to 2*. I am taking a 15* bag.

Does using 2 sleeping bags work?...assuming you don't crush the down and allow it to loft.

I have a montbell 15* and a 40*. The 40* weighs 1lb so it's not like it's a big deal if bringing it will help.

MTS

[Manwich]

If it works, it works... The insulation will certainly double up in your favor. To what factor, I cannot say, but you'll be clear to 2*.

[Grinder]

c. a year ago, on the Hammock forum, there was a formula giving the equivalent degree rating for a doubled up bag set up. also a nice discussion about the factors to consider.

Grinder

[Manwich]

http://www.hammockforums.net/forum/showthread.php?t=297

I decided to take this combination and post it for future reference for other in the article section here.

This came from "Peter_pan".

A 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 bag rating subtract it from 70, divide that number by two and then subtract it from the first bag rate for a combined value ex

Two 40 degree bags... 70-40 =30 divided 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.

I suppose this was what you were talking about?

Fixed his English errors and crunked this out, sciency, ain't it?

Pan's Insulatory Factor:
x - (70 - y)/2 = z

x = first bag
y = second bag
z = rating of doubled bags

So in this case: 15 - (70 - 40)/ 2 = 0
So according to this theory (which seems about right to me) doubled up you've got a 0* system

[mts4602]

Thanks. I found one of the threads on the hammock forum but not this one.

http://www.hammockforums.net/forum/showthread.php?t=297
I suppose this was what you were talking about?

Fixed his English errors and crunked this out, sciency, ain't it?

Pan's Insulatory Factor:
x - (70 - y)/2 = z

x = first bag
y = second bag
z = rating of doubled bags

So in this case: 15 - (70 - 40)/ 2 = 0
So according to this theory (which seems about right to me) doubled up you've got a 0* system

[The Solemates]

http://www.hammockforums.net/forum/showthread.php?t=297
I suppose this was what you were talking about?

Fixed his English errors and crunked this out, sciency, ain't it?

Pan's Insulatory Factor:
x - (70 - y)/2 = z

x = first bag
y = second bag
z = rating of doubled bags

So in this case: 15 - (70 - 40)/ 2 = 0
So according to this theory (which seems about right to me) doubled up you've got a 0* system

wow. i cant really say more.

but i'll have to admit the engineer in me finds this fascinating.

[The Solemates]

wait a minute the answer is -7.5

somebody clue me in

[Manwich]

Note, I think you'd make the Higher Rated (Lower Degree) bag first, because if you switched the x and y, you'd get 12.5

[deadhorsejoe]

Big Agnes uses an over bag system with their sleeping bags. For example , their website says that using their 40 degree Yampa adds 25 degrees of protection to the bag you put into it. I have several of their bags (Lost Ranger (15 deg - really more like a 25 degree at best) , Yampa (40 degree), Lost Dog (50 degree) but have never used any of them together.

[JAK]

For what you propose I think its worth doing for sure as long as they fit reasonably well. I would normally say no, because you are adding 12oz of shell and only 6oz of down, but because its 800 fill, and the 'huggy stretch' design think it might work very well. I think you would be just as well protected by wearing 18oz of wool underwear, but if you have the Montbell 40 and don't have the wool underwear I say go ahead with what you've got.

[buz]

Bring them both, being cold at night suks big time. You can use the 40 degree as quilt over your warmer bag if it has full zip, just stuff the foot section inside each other, zip up partway, keeps the rest of the bag centered. Have a good hike.

[berninbush]

x - ((70 - y)/2) = z

x = first bag (higher rated/lower degree)
y = second bag (lower rated/higher degree)
z = rating of doubled bags

Extra set of parenthesis to make it crystal clear that the x is not divided by 2, just the 70-y part. I think you're correct about the order of operations implying that anyway, but the parenthesis makes it clearer for anyone who hasn't had math in a while!

[dradius]

wow, I have a deep hatred for math equations, but this is really cool. thanks.

[twoshoes06]

What a nice equation. I have not seen that before.

Anyways, I have a Western Mountaineering 20 and 45 degree and they easily keep me warm down to 0 degrees. I would take both and use them, especially if they don't weigh much. I would rather be warm with a layer to take off than cold with nothing to put on, but that's just me.

[Wise Old Owl]

Going to put this out there, forget the formula's, get the bag you want, carry a light polypro leggings and long sleave shirt in winter version polypro. And here is where I am going out on a limb. Carry a less than 1lbs down jacket compressed into the same bag as your sleeping bag. not for hiking in, it would absorb sweat. This is when you are in camp and trying to keep warm. So here you go.. Put the jacket on jump into the sleeping bag enjoy .. too cold? pull the bag up and over or dive deeper.... warm? pop out without the confinement of the bag. The jacket is your second layer. Where did I get this info? from a lightweight backpacking book at REI. It discussed a sleeping bag as an "elephants foot"

Then enjoy your hike.

[Blissful]

This math is beyond me...



If it works, take it. Some guy in '07 - Zero I think, was trying to go with two bags, he wasn't too successful I didn't think and was still cold.

[nitewalker]

i stayed out at black gap shelter on monday, hawk mtn shelter on tues and gooch on wed nite using the two bag system. i had a ems mtn lt 20* and a mtn hdware phantom 45* bag. all three nites were pretty darn cold. my two gatorade bottles holding water both froze nearly solid. the two bag system didnt even flinch at the cold and i will bet it got down to 5* or lower on the mtn. i actually woke up a little sweaty one of the nites. bring the two bags, u cant lose that way... being cold does suck. i was a little cold the week before up in the area of upper goose pond with my ems 20*...