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Best 2-bag Sleep System for Deep Winter?
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Max Dilthey
(mdilthey) - M

Best 2-bag Sleep System for Deep Winter? on 06/25/2013 19:12:44 MDT Print View

Forgive the deep winter question in June, but i'm purchasing now!

Last winter I used a Mountain Hardwear Ultralamina 45* bag inside of an EMS Solstice 20* bag and went to -10*, so the system worked. However, the EMS bag weighed a ton and I didn't really need it to be synthetic because almost every time I used it, it was snowing and not raining or misting.

So if I replace my Solstice 20 synthetic with a Western Mountaineering Highlite 35, will using it inside the MH Ultralamina 45 prevent the cold spots from sewn-thru baffles well enough to essentially negate the issue?

For the lazy:
MH Ultralamina 45 inside Solstice 20
WM Highlite 35 inside MH Ultralamina 45

I know i'm losing about 15* (not close to exact), but I think the WM bag inside the Ultralamina may have a much higher warmth rating, so to speak, due to the cold spots being covered.

Is this a valid conclusion?

Chris Bowman

Locale: ORF
logic? on 06/25/2013 19:25:07 MDT Print View

Dont know if it is a valid conclusion or not, just questioning the logic of 2 bags rated 10 degrees apart. Why not get one instead rated to atleast 20 degrees. Do you want to carry 2 bags if temps down to 20 are expected?

If it were me, I would get a 10 degree bag for winter, you already have a 45 for summer, and you could double those up for really cold.

I know I didnt answer your question, just offering my opinion.

Tad Englund
(bestbuilder) - F - MLife

Locale: Pacific Northwest
Re: Best 2-bag Sleep System for Deep Winter? on 06/25/2013 19:37:39 MDT Print View

Max here is a formula that was on here a while back
Two Sleeping Bags

The formula provided [x – ((70 - y)/2) = z] provides this:

MH Ultralamina 45 inside Solstice 20
X= 20* bag
y= 45* bag

X=20* and Y=45* : 20-((70-45)/2) = 7.5*

WM Highlite 35 inside MH Ultralamina 45
X= 35* bag
y= 45* bag

X=35* and Y=45* : 35-((70-45)/2) = 22.5*

Yes the baffle issue would go away if used under the MH, but you still have a loft issue. And loft is where you get your warmth.

Edited by bestbuilder on 06/25/2013 19:38:11 MDT.

Max Dilthey
(mdilthey) - M

WM Options on 06/25/2013 20:06:37 MDT Print View

Opinions outside the realm of the question are welcome.

Fro what I've read, the baffling and down is so high-quality on the WM that it's practically a 25º already. However, the sewn-thru baffles keep the rating down. So my hypothesis is that if you cover the cold spots then the bag's warmth rating rises substantially.

Loft, to my knowledge, depends on how I fill out the bag, and I am skinny. However, it is a concern. I know that loft is gonna be the make-or-break, but given the sewn-thru baffles, I don't think the Ultralamina inside the WM bag is going to come close to the warmth of my old system.

I could buy a 10º bag, because then my system for 30º+ weather would be the 45º and a coat.

My personal furnace means I can push any bag between 10 and 15 degrees or so.


My other option is to spend an extra $100 and get a WM MegaLight and use that as the outer bag. No loft issue, no baffle issue. But I like the weight on the HighLite, and would rather use that.

Any opinions on the HighLite as the outer bag?

Edited by mdilthey on 06/25/2013 20:08:29 MDT.

John S.
(jshann) - F
Re: WM Options on 06/25/2013 20:16:11 MDT Print View

Highlite not large enough to be an outer bag. It should e the inner bag with a quilt over it.

Richard Fischel
call feathered friends on 06/25/2013 20:20:01 MDT Print View

and ask them to make you a great auk. not listed on their site, but they still have the pattern. wm made something similar, the pod 15 and 30. the pod is out of production but if you watch the auction site you can snag one. i've never been a big agnes fan, but they make a couple of bags that would work. These all fit into the no insulation on the bottom, over-bag catagory. they are roomy enough to not compress the inner bag and can be used alone in warmer weather.

Max Dilthey
(mdilthey) - M

Clarification on 06/25/2013 20:44:43 MDT Print View

I wish I could afford to buy the perfect two bags, but I am only buying one bag; A 20-30º winter bag. I could buy a 10º bag, but my gut tells me to err on the side of versatility, and a 20-30 goes a lot farther on other UL trips. I am willing to revert this opinion.

If there's a way to make this bag the HighLite, that's the way I want to go, because the weight is so awesome.

But if the physics/thermodynamics don't add up, obviously I will have to reconsider.

Edited by mdilthey on 06/25/2013 20:45:47 MDT.

Ian B.

Locale: PNW
Re: Clarification on 06/25/2013 20:58:01 MDT Print View

I think the theory is sound but as mentioned above, compression may become an issue. The USGI sleep system was designed (albeit synthetic) this way and I alway appreciated how versitile it is. Unfortunately there is a hefty weight penalty to go with it. What you are proposing sounds like a great idea.

I'm 6'3" but my shoulders are ~62/3" which limits my choices of lightweight sleeping bags. After a lot of research, I pulled the trigger on a Mont Bell UL Super Spiral #3 due to the way it eliminates dead space and stretches out to 81" at the shoulders. You may want to give them some consideration as your outer bag.

Look forward to seeing the final product.

Max Dilthey
(mdilthey) - M

Good Call on 06/25/2013 21:01:33 MDT Print View

Thanks, I will!

I am a bit smitten with the WM's ~16oz weight, but that's a helluva second choice. Great bags, those spirals, if memory serves.

I think the only way to solve this is testing...

David Goodyear
(dmgoody) - MLife

Locale: mid-west
bag/quilt on 06/25/2013 21:56:37 MDT Print View

a bag/quilt combo is more versatile. I used a -20 MH lamina with a 25 deg enlightened equipment quilt over it and was comfy down to -38 F. The cool thing is that the moisture layer moved into the quilt nad I was able to dry it out while eating breakfast. (used as a blanket)



Bob Bankhead
(wandering_bob) - MLife

Locale: Oregon, USA
bag/quilt on 06/25/2013 22:07:29 MDT Print View

WM will overfill the bag of your choice if you special-order it through a dealer.

Max Dilthey
(mdilthey) - M

Overfill? on 06/25/2013 22:12:46 MDT Print View

I don't know if overfill will do the trick, if there are cold spots from sewn-through baffles then I can only increase the warmth of the HighLite as an outer bag by so much, I believe. If I'm wrong, though... That could be the ticket?

eric chan
(bearbreeder) - F
Re: WM Options on 06/25/2013 22:27:26 MDT Print View

Fro what I've read, the baffling and down is so high-quality on the WM that it's practically a 25º already.

no its a 32F bag for the EN LL rating ... all the positive BPL thinking wont chance that ;)

if figure 15-20F + if you add your 40-45F bag over the main bag ... so ~10-15F for the"average" person

Max Dilthey
(mdilthey) - M

Theory on 06/25/2013 22:36:17 MDT Print View

That's alright with me, I was hoping it would be closer to zero because my understanding was that the WM bag's sewn-through construction was sucking a few degrees away from the rating, and if covered, would result in a higher warmth level.


Edited by mdilthey on 06/25/2013 22:36:53 MDT.

(KalebC) - F

Locale: South West
2 bags on 06/25/2013 22:47:38 MDT Print View

I don't see the point of bringing 2 bags, unless its a cost issue. I have a 15F bag and have used a down puffy jacket and pants to get into the single digits. If its that cold I bring down garments anyways. "Pack less, be more"

Max Dilthey
(mdilthey) - M

Cost on 06/25/2013 22:52:13 MDT Print View

Cost issue. It's potentially 30 degree bag weather 3/4 of the year, and I already have the summer 45 degree synthetic for wet summer sleeping. So if I can get a 30, it's like buying a winter bag and a 3-season (but I need to do it right!)

I spent a 30 degree night in a twenty-year-old Quest 50+ summer bag that was 5.5 feet long. I'm 6'2". I did it in Smartwool Midweight and an Arcteryx SV Atom, and slept cold, but I slept. I can deal with a lot and still sleep. I just want to cut weight now.

Franco Darioli
(Franco) - M

Locale: @Tarptent
Best 2-bag Sleep System for Deep Winter? on 06/25/2013 23:11:22 MDT Print View

With a typical thermal top and bottom layers (T and pants) the Highlite is a 35f bag.
If you read about lower temps it is because they are using puffy layers with it or just kidding.
(I had one and no I am not a cold sleeper)
I get to 20f with the 32f rated Summerlite (yes it is warmer than the Highlite) but that is with socks,puffy top and bottom and Merino hat and Merino gloves .
My top (WM Flash) has a hood too...
And that is my way of saving weight on a sleeping bag.
As mentioned above the Higlite would be too small as an outer bag even if you are very slim.

Max Dilthey
(mdilthey) - M

The dream dies. on 06/25/2013 23:29:35 MDT Print View

Good to know on it not being an outer bag. Unfortunately, the MH Ultralamina is a bit snug too..

Alternatives (spiral hugger on the list) welcome!

Mike W
(skopeo) - F

Locale: British Columbia
Best 2-bag Sleep System for Deep Winter? on 06/26/2013 00:35:23 MDT Print View

I went with the Montbell Stretch bag as the over-bag because I wanted to use my old down bag in combination with the Montbell for colder weather camping. For me it made sense because I already had another good quality down bag to use for the inner bag and I just don't do enough cold weather camping to require a dedicated cold weather bag. The old down bag is a slim fit and the Montbell Stretch bag fits over it very nicely and doesn't compact the down of the inner bag at all. I also remember Richard Nisley mentioning that air gaps between two fabric layers will act as a minor insulation layer as well, so you probably gain a bit of warmth by using two bags in combination if the outer bag isn't too tight.

Edited by skopeo on 06/26/2013 00:42:18 MDT.

Hiking Malto
(gg-man) - F
Two bags vs ? on 06/26/2013 05:29:08 MDT Print View

The two bag concept, while not perfectly optimized, is a great option for folks that don't want to have all their gear season specific. I love the concept of using a single set of gear and adding or subtracting vs. replacing. Having said that a couple of possibilities.
1) I would look at getting a quilt as your outer layer vs a bag. I suspect most bags will lose too much insulating power due to compression.
2) there are other options such as warmer clothes, a bag liner and my favorite VBL. I experimented with VBL last winter and this will be method of extending my normal three season setup down into single digits or possibly below. I personally believe this may be the biggest bang for the weight and buck. I use my cuben rain suit as VBL so I am carrying it anyway.

There may be a better way to achieve your desired outcome. I'm assuming you have already looked into down booties and hats. And a good mat system will also go a long way at keeping you warm in the winter as well. Good luck.

rOg w
(rOg_w) - F

Locale: rogwilmers.wordpress
deleted on 06/26/2013 06:18:33 MDT Print View


Edited by rOg_w on 09/08/2013 16:23:22 MDT.

Max Dilthey
(mdilthey) - M

Clarification on 06/26/2013 08:26:37 MDT Print View

Thanks for the measurement Rog, but I don't own any WM bag yet, and I can only buy one.

It looks like the measurements are the following:

Mountain Hardwear Ultralamina 45º: 60in Circumference

WM Highlite 35º: 60in Circumference

WM Megalight 30º: 65in Circumference

EMS Solstice 20º: 62in Circumference

2 inches isn't too bad on the Highite, but Megalight may be the way to go.. I can probably use the HighLite as an outer bag. Will cold spots prevent deep winter use, or are the sewn-thru baffles not a big deal if I have a coat and the 45º bag?

Dharma Dog

Locale: The Louisiana Swamp
Re: Clarification on 06/26/2013 08:32:36 MDT Print View

FYI - Western Mountaineering bags including the Megalite are on sale right now at

Max Dilthey
(mdilthey) - M

Sale on 06/26/2013 08:53:26 MDT Print View


Dustin Short
(upalachango) - MLife
Re: Sale on 06/27/2013 14:45:24 MDT Print View

I would get a 20F bag with full baffling like the WM Ultralite (I do own it and love it).

This is my reasoning:

With a a 45synth bag you are covered for wet summers. When the temp cools down a bit you can supplement with puffy clothing and probably get down to freezing easily (and the puffy clothing is nice in those chilly morning/nights). This I think is near your rationale.

Going from above freezing to below is a huge difference in perceived temp, because now you're body is moving from fighting hypothermia to fighting frostbite. So getting a 30F bag only lets you "play" around this significant temperature. You usual light insulation clothing for near freezing temps will let you push your bag colder, but you won't get the same 10-15F boost as you do when temps are all above freezing mostly because quality light 30F bags have sewn through baffles (as in the 45F down to freezing).

This is where I advocate a 20F bag. It gets you well into freezing temps. When the forecast calls for freezing nights, a 20F bag is warm enough to sleep comfortable should those all too frequent cold snaps occur, but not so warm that you can't sleep in 40F temps too. Then if you need, you can push a 20F bag down to 15F or 10F with light puffies and even further if you go with heavier weight insulation as forecasts dictates.

If you can take a synth 20 bag down to -10F with your MHW 45F then a proper 20F down bag will take you to same temps if not colder, with a considerable weight savings.

So with these two bags you will have solid coverage between -10F and 55F or so (based on your experiences) which is impressive. There really aren't too many holes in that range where you'll be uncomfortable, especially if you supplement with your clothing. It will make your EMS bag redundant but sell it off to friend or keep as a loaner.

Now for a specific bag, the WM UL has a trick, it's actually EN rated to ~16F and thus a very warm 20F bag for a full pound savings on your EMS. It is pricey but I've not regretted my purchase once (ok, maybe summer in the desert...but a MYOG quilt is in the works). I've slept as warm as 50F in it and it vents well enough.

For reference this is my system; unfortunately I don't get many chances to test "really" cold temps or soggy conditions in the desert so take with a grain of salt and I am conservative since I hate the cold (although slowly adapting). Pretty much the WM UL for all temps I routinely see. In the heat of summer I've got the synth quilt in the works which will also be used in wet conditions. If the forecast calls for 20F but I'm at elevation, the synth quilt comes along as extra protection for cold snaps. With appropriate clothing for the season I'm fairly confident that I can get down to 0F using these two (my synth quilt is lighter than a MHW 45F). I'm sure playing with VBL would go further. I did just pick up a 0F bag to test this upcoming winter but I expect it will be relegated to deep WY winter conditions or high altitudes since the rest of my system is so versatile.

Max Dilthey
(mdilthey) - M

Woohoo! on 06/27/2013 14:52:42 MDT Print View

I think this is probably the most helpful post possible. Your insight with the difference between 20 and 30 is invaluable. Thank you for taking the time to write this. My question is essentially answered.


Raymond Estrella
(rayestrella) - MLife

Locale: Northern Minnesota
Best 2-bag Sleep System for Deep Winter? on 06/27/2013 18:37:01 MDT Print View

I agree that a bag/quilt combo will give you move options and a greater range of use. Check out this review I did of a 0 F bag:

I used a couple different quilts with it. My son too has used some of my quilts along with his 20 F Sierra Designs bag to take it below 0 F a few times.

Enjoy whatever you do decide to get.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
Synthetic outer, down inner on 06/28/2013 14:09:34 MDT Print View

My extreme cold weather system is an older -20 F. MH Polarguard insulated bag with a zippered expanding gore so I can insert my WM Megalite inside. This combo does not compress the down bag and is not restrictive.

Down inside and synthetic or DWR treated down outside means that your body moisture, when migrating to the outer layer (& THEN CONDENSING), will be in a layer that is not as much affected by moisture and likely let the frozen moisture at least sublimate off to the atmosphere when the bag is aired. Further, double bags can be separated for better airing.

Personally I feel every down winter bag should have the down fill treated with one of the new down DWRs. Patagucci seems to have one of the best of thse treatments but, Mon Dieu! the $$$.

Edited by Danepacker on 06/28/2013 23:06:00 MDT.

Raymond Estrella
(rayestrella) - MLife

Locale: Northern Minnesota
re: DWR down for winter on 06/28/2013 20:37:31 MDT Print View

"Personally I feel every down winter bag should have the down fill treated with one of the new down DWRs"

Why? At -20 F you aren't going to fall in a creek or get caught in a rain storm.

If you have condensation in the bag freeze, it will do so in whatever insulation you have, DWR or not.

I like the tech, but don't see it useful/needed at extreme temps.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
DWR treated down for winter bags on 06/28/2013 23:12:21 MDT Print View

My Dear Raymond,

Down bags in winter have the dreaded "outer shell condensation" problem. Believe me, without the ability to get rid of this frost your down bag gets progressively heavier each night, eventually becoming unstuffable and unuseable over weeks. (See Scott's disasterous South Pole attempt).

A DWR treated down MAY let this frost detatch from the down more easily and MAY sublimate if exposed to sub zero airing daily. (I'm surmising here.)

I've experienced frost buildup in both down and synthetic in sub freezing weather over many days. It ain't fun and it ain't warm.

Raymond Estrella
(rayestrella) - MLife

Locale: Northern Minnesota
frost on 06/29/2013 03:09:32 MDT Print View

Yes, I know that Eric. (And it happens with any bag, not just down.) The only way to "get rid of it" is to let the bag thaw so you may be right that it could help there. But when it never gets above freezing it would be hard to get to the point of needing the DWR down, right?

Well I am off to Paul Bunyan State Forest for a few days. No frost in the forecast, just heat, humidity and huge mosquitoes. Have a good weekend.