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Sleeping bag liners

I’m looking for recommendations on the warmest sleeping bag liner people have used, so I can get out and camp in my NEMO Sonic 0F. Being about a 10F bag, and with overnight temps on the mountains dropping to at least that low, I’m looking for something that will help me sleep a little warmer until someone has the WM bag I want in stock. It needs to be fairly large, my Sonic has a 69” inside shoulder girth and I’m about 59” around the shoulders. 

My experience with liners is that they don't add enough warmth for you to be able to rely on. In other words, if your bag keeps you comfy to, for example, 10F, then if the forecast calls for lows of 15-20F then it might be a good add in case temps get a little colder than expected. But of the forecast is for 5-10F I would not rely on a liner to make up the difference in comfort because your campsite might hit 0F that night.

My personal approach would be to wear thicker or doubled up baselayer and insulation layers.

For winter camping the mountains, I have used a pad with high R value on top of a ensolite type pad.  Then I use a 20 degree rated down bag, with a small fleece blanket inside on top of my body.   A warm dinner, a fire before bed, and a really warm dog musher's hat makes it comfortable.  I usually don't camp in temps below about 10 above.   Wearing a vest and a coat and dry clothes help a lot. 

It also helps to camp in a sheltered spot in the woods with small trees around for a wind break and thermal protection.  It is exactly what large animal species do in winter. 

Eat a high calorie snack that contains protein, right before bed.  Digestion produces a significant amount of heat. 

If you are only out for a night or two, wrap your bag in a plastic tarp.  It provides a substantial increase in warmth.  Unfortunately it also traps moisture in the bag, so this approach won't work beyond a weekend outing.

You'll probably have trouble inserting anything bulky in the bag, given the confining interior of most bags and your large girth.  You can always add a blanket over the top and a reflective ground cloth beneath 1" thickness of dense closed cell (winter version) blue foam pad or equivalent.


I really hate wearing more than a thin base layer, anything more is uncomfortable but I can do it if necessary.

I also have the option of using my WM EverLite summer bag as an inner bag. WM states it can add about 10F of warmth, which is what I generally hear a liner is good for.  

My sleeping pad is one place I’m all set, I have an Exped DownMat 9 with an R-value of 7.8. Whenever possible I use denser vegetation, a snowbank, etc, as a windbreak, but a lot of the places level enough to camp are pretty open. I suppose I should add a shovel to my kit so I can dig in and build a snow wall. Hopefully I can find the -30F bag I want soon and not have to bother with all this LOL

only liner i have ever used that provides notable additional warmth was a vapor barrier. they're an acquired taste because they feel clammy and humid, particularly if you're not used to them, and i don't like them. But, they add some warmth and keep moisture out of your sleeping bag insulation.

Bivy bags help a little, but they're often bulky, and the outer edges of your bag can get damp then frosty. 

problem with a liner of any reasonable loft is that it can end up compressing your sleeping bag from the inside, so you might not benefit. 

real cold, i use a mountain hardwear down bag that's rated to -40. have slept in it down to -25/30f, it's a good bag. If you might consider looking for a premium alternative, try the Valandre Odin or Thor.  I would call to get a handle on the dimensions, but the build quality and fill are on par with Western Mountaineering & Feathered Friends.  

Out of all the subzero bags I’ve looked at, by WM, FF, Marmot, Rab, Mountain Equipment, TNF, etc, only NEMO and WM had bags big enough for my upper body. Of course, Nobody has any of the ones that fit me. In my 68” inside girth Sonic I have maybe 1.5”-2” of room at my shoulders, it’s hard to tell for sure because the fabric obviously has some give to it. Before I bought my NEMO  I tried bags in the 64” shoulder girth range (WM Bison was one) and they were way too tight. I couldn’t even get the Marmot Cwm zipped past my waist (48” hip circumference with the tape held loose.) Maybe something with a 66” shoulder girth (S2S Alpine III -40, for example) would work since each inch of “diameter” is 3.14” of girth, but I think I’d be stuck with my arms straight by my sides and maybe able to put my hands on my stomach. 

Summer at WM has been helping me, she gave me the names of the retailers they shipped their last batch of -30F Cypress bags to but none of them have any in stock. She also suggested using my EverLite as an overbag instead of bringing it in the NEMO, by closing the foot drawstring, zipping it up a foot or so, and using it like a quilt, so I think I’ll be bringing it along when I finally have a free weekend that’s not rainy and has forecasted lows between 0-10F. 

I guess I missed your post when I replied last night, Ed, and until now didn’t see what was before that reply. My problem isn’t staying warm in general, just with this particular sleeping bag in the temps we see here. The last time I did any real winter camping was when I was stationed in Germany, and that was 1992-95. I was also in beast condition then, a friend on another post about 11 miles away would go hiking and camping in the large training area there. I’d hump my large ALICE, loaded with extreme cold sleeping bag, shelter half, and other gear the 11 miles to meet him then we’d head out. I don’t ever remember being cold in that 15lb bag of feathers, but was definitely uncomfortable from just a 1/2” thick CCF pad between my back and the hard ground. 

A lot of times I’ll reconstitute a second dinner right before bed, it’s helped with my 45F bag in mid-30s temps. Sometimes it‘s an actual dinner entree, other times oatmeal with walnuts, almonds, or unsalted sunflower seeds added.

This 12 day forecast for Boundary Bald Mountain (maybe 5 miles away) is the main reason I want a good -30F or so bag! Some nights have winds forecasted that I wouldn’t want to be in even in the best weather, but most of the rest of those nights I should be nice & comfy in one.

Well said

May 16, 2022
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