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Using two sleeping bags
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Cesar Valdez
(PrimeZombie) - F

Locale: Scandinavia
Using two sleeping bags on 07/14/2011 15:19:41 MDT Print View

I did more cold weather camping over the last few years and have really enjoyed it, even when I was still packing traditional. In a few months I will finally have a 3 season down bag (4C temp rating, 800g)--my first!--and am looking forward to switching it with my syth 3 season bag (6C temp rating, 1200g). It got me thinking... what if I were to use both bags at the same time for extreme winter camping? Last winter it got down to -20C in my area. Would using both my down and syth bag together work? And how should I use them, down on the inside or outside?

Any winter campers try anything like this?

eric chan
(bearbreeder) - F
down inside on 07/14/2011 15:22:09 MDT Print View

down inside synth so that the synth outer takes the moisture that travels outwards

as to an exact rating, i leave that to the experts ... i generally assume an additional 20F or so from adding a summer bag to another bag ...

(cuzzettj) - MLife

Locale: NorCal - South Bay
RE: "Using two sleeping bags" on 07/14/2011 16:08:52 MDT Print View

The rating will depend on compression and loft also. Check the fit of the two bags and weather or not one compresses the other. I also agree. The down handles the sweat moisture much better than the synthetic.

Ultra Magnus
(Ultra_Magnus) - F
Re: Using two sleeping bags on 07/14/2011 16:24:42 MDT Print View

Maybe this will help you estimate how much warmer it will be -


Walter Carrington
(Snowleopard) - M

Locale: Mass.
Using two sleeping bags for winter. on 07/14/2011 16:47:48 MDT Print View

Down inside the synthetic.
Water vapor will travel from your body outward till it reaches a temperature where it will condense into water. It is best if this point is inside the synthetic bag. If you use a vapor barrier liner, it will matter less, but probably still better to have the down bag on the inside. How well it works depends on how much you're compressing the inner bags loft and on air leaks (winter bags are better sealed, baffles,etc.).

I considered this approach but ended up getting an EMS -20F bag on sale; this is a pretty good bag. It's worth checking EMS online regularly for sales on these bags.

Mark Primack
(Bufa) - MLife

Locale: Cape Cod and Northern Newfoundland
Two bagger on 07/14/2011 17:28:51 MDT Print View

Maybe 20 years ago EMS used to sell a lightweight down liner bag/summer bag rated at 45F and a coordinated down three-season bag rated at 20F that were designed to work together as a winter bag. EMS rated the pair for -30F. The summer bag was cut tight and the three-season bag was cut large so that when used together the three-season bag wouldn't compress the inner bag. I used it to -38F. I sold it to an acquaintance seven years ago and he was still using it on a winter trip we did earlier this year. Together the bags weighed around 6lbs.

I currently have two MB bags, 15F #1L and 40F #3. I am hoping and expecting to use them together down to -20F at a combined weight of 3.4, though I may need to use my down top and bottom.

Edited by Bufa on 07/14/2011 17:30:09 MDT.

Aaron Sorensen
(awsorensen) - MLife

Locale: South of Forester Pass
Re: Two bagger on 07/14/2011 19:35:57 MDT Print View

I can tell you 15 + 35 = 0

I use my 15* long bag, (I'm 5' 11") with my 15 ounce quilt and can be comfurtable down to 0*

It's not just loft, it's also being able to fill in all the voids that a single bag can not. Having the bag in a bag fills in those voids very well.

Chad "Stick" Poindexter
(Stick) - F

Locale: Wet & Humid Southeast....
Bag + Quilt on 07/14/2011 20:24:37 MDT Print View

I plan to layer my summer quilt with my Marmot Helium if I ever decide to go out in (expected) temps less than 10 F. I am hoping that by draping the quilt over my Helium I should be fine to temps around 0, but I haven't got to test this out yet...unfortunately our daily temps are now over 100 F so it may be a little while... This combo should be right at 3 pounds.

However, if I ever start going more frequently into temps lower than this I plan to get a WM Kodiak...

Justin Baker
(justin_baker) - F

Locale: Santa Rosa, CA
"Using two sleeping bags" on 07/15/2011 01:10:15 MDT Print View

I did this but I was surprisingly a little cold. It was with a usgi patrol bag and a lamina 35 bag. I have a feeling this was due to compression.
A lot of military sleeping bag systems use the bag in a bag system, but they are made and properly sized for that. You would have to experiment with the bags to see if they compress or not. You could always try unzipping one bag and laying it over you like a quilt.

Jeremy Osburn

Locale: New England
Re: Using two sleeping bags on 07/15/2011 06:57:31 MDT Print View

I don't necessarily agree with putting the synthetic bag on top. Most likely which ever bag is on top will stay dry. In temps as cold as -20C your body temp shouldn't be able to push vabor through 3 fabric layers before it condenses. Also the new down bag is lighter so most likely won't compress the heavier sythetic bag as much allowing you to capitalize on more loft. The most important thing is loft so take the two bags and open them all the way up and layer them together and see which layering gives you the most cm of loft. My guess from when I did it with a 3 season down bag and a summer synthetic bag, is that your down bag will be on top because it is lighter. When you go to test it you want to fully zip up the inside bag and use the outside bag as a quilt overtop.

The most important thing however is to test it in your "back yard". I don't really think you can do any amount of math to come up with how cold the 2 bag system can take you. Too many variables, your body, loft, compression, vapor... Just test it on single overnights until you hit either as cold as you want to go or as cold as the double bag will take you. Eat a big meal too!

Also you can try a vbl (emergency foil bivy) but they are hit or miss. I really don't like them at all. Don't underestimate the power of the sun it may be -10C out side but in the sun with a little breeze a bag will dry out enough to retain its loft for several days of a trip.

Edited by earn_my_turns on 07/15/2011 07:00:48 MDT.

Will Webster
Slips off on 07/15/2011 08:58:12 MDT Print View

Last winter I tried laying a MB Thermal Sheet (fully unzipped) over a WM Summerlite. Seemed like a good idea in my living room but I'm too restless a sleeper - the MB "quilt" just slipped off the bag. The slippery fabrics didn't provide enough friction to keep the upper layer in place when I moved around.

eric chan
(bearbreeder) - F
down synth on 07/15/2011 10:46:25 MDT Print View

there has been at least a thread or two here where someone used down over synth and ended up with a moist bag

as to water vapor traveling outwards in cold env and condensing .... it happens wherever the dew point is in yr system ... most overbags manuf wll tell you explicitely to use the synth overbag on the outside ... also when dealing with loose snow and condensation in the tent synth on the outside protects the inner down ...

compression is a potential issue when layering any down system ... clothes or bags ... size appropriately

Chad "Stick" Poindexter
(Stick) - F

Locale: Wet & Humid Southeast....
down over down on 07/15/2011 11:00:14 MDT Print View

So is it a bad idea to layer a down quilt over a down bag?

Edited by Stick on 07/15/2011 11:00:49 MDT.

eric chan
(bearbreeder) - F
down down down on 07/15/2011 11:14:26 MDT Print View

yr outer down layer may well get a tad moist ... if you can deal with that its up to you

big agnes pimping some of their down bags for overbag use aside ... you dont see that many down overbags these days, or i dont

i suspect theres a reason for that ...

if its that cold you can avoid the issue entirely with a cheap VBL

Cesar Valdez
(PrimeZombie) - F

Locale: Scandinavia
What about adding cotton liner? on 07/19/2011 01:23:07 MDT Print View

Good feedback here, I am going to experiment in my backyard before going out next winter. But something else came to mind. I also have a cotton liner that I use at times to up the temp on my syth 3 season, but should I use it with my down bag? Or with the down bag/summer syth bag combo in the winter?

If I do use it, where would be best? As my first layer, over the first bag, or over the 2nd bag? Or should I not use it at all?

I am leaning towards having the summer syth bag on the inside because it is tighter and I like the idea of having more loft in the down bag.

Thanks for all the insights.

Matthew Marasco
(BabyMatty) - F

Locale: Western/Central PA, Adirondacks
re: on 07/19/2011 03:22:55 MDT Print View

I did this over the winter using two bags with a total of 19 oz of 750 fp down. I was more than comfortable to temps as low as 12 degrees (inside a double-walled tent).

Jeremy Osburn

Locale: New England
Re: What about adding cotton liner? on 07/19/2011 06:24:52 MDT Print View

I would skip the cotton liner. My big concern is that it would get moist at night from vapor and then freeze during the day. Once frozen you wouldn't be able to thaw and dry it until the trip was over. The general rule of thumb about cotton kills is especially true in winter, where it sucks the heat out of your body and never dries. Your best bet for adding a light weight temperature bump is an emergency bivy vbl which I don't like using but many people do (claimed up to 10 F in temperature gain), vbl clothing which I hope to try next winter, or a silk bag liner on the inside. I think the claim on those is that you get a few degrees of warmth added, but I have never used one so I can't say for sure.