If you had a 40 degree bag...

[Brooktrout]

One of my friends asked me for a sleeping bag recommendation for an upcoming BWCAW trip in January and I wondered what everyone here would recommend.

He currently has a 40 degree down bag that he could incorporate in his setup.

Think 40 is too warm to be useful in a 2-bag system? If you had to incorporate the 40 degree down, what would you get as a second bag to complete the setup? Down? Synthetic? Temperature?

I've been happy with my sleeping bag setup (8 degree down bag inside an old 20 degree synthetic, with an exped synmat sleeping pad). I have ideas about what to recommend, but wondered what everyone else thought...

We'll be hot tenting and should have the ability to dry things out, though I never count on it.

[eatTHEcurry]

I had an old 20 degree rei down sleeping bag, and put that inside my northface blaze synthetic sleeping bag. Was pretty cold sleeping at 9 degrees. The down bag was dry and the synthetic picked up the condensation from my breath. I would recommend something modular and purpose built that has a core bag and an overbag. Wiggys makes something like this and of course military surplus mss bag. The thing I didn't consider was that you're limited in space by the size of the inner bag. My down bag is a snug fit for sure, so I had very little room in it for any layers, or even to toss and turn. Arguably that made things far more uncomfortable than the actual cold.

[Brooktrout]

My friend ended up unable to make the trip, though now you've got me thinking about a Wiggy's bag : ) ...Good point on the space consideration. I'm always entertained with experimenting with different bags. Thanks for the thoughts.

[eatTHEcurry]

Yeah its one of those things to consider, plus you may want a larger bag to keep clothes warm in, or accommodate you wearing more layers.

[4estTrekker]

Not sure if this is helpful to your initial question or not, but I have a 0F (more like 15F, but meh) hydrophobic 800 FP goose down mummy sleeping bag that is my go-to base. I then have two different Climashiled Apex quilts that I built long/wide as well to go over/around the sleeping bag in proper cold. One is rated for about 15F, the other for 0F (that's only when sealed up like Fort Knox). I like the synthetic on the outside because it transfers the dew point outside of my down bag and inside the synthetic insulation, which can handle it better over multiple nights. It also bears the brunt of condensation from exhalation. Plus, quilts are easy to vent to regulate moisture, or to pull up quickly after the stove goes out and the tent temp drops. Climashield doesn't pack as neatly as down, but man, I love the stuff. I can fit my big ol' chonky 0F quilt and my down bag inside my backpack, which I always carry anyway. This makes for a light backpack on the treks in/out and frees up precious space on my toboggan. I line the backpack with a trash compactor bag to keep the contents dry.

[hurricanebob]

A double-bag system is easy to put together as long as the outer bag is big enough to accommodate the inner bag without compressing loft on either bag. It doesn't matter so much whether either one is down or synthetic unless you are staying out for a long time. If you have a semi-rectangular bag, that's the outer bag; the inner can be the three-season mummy bag you normally use.

In sleeping bags, warmth is a function of loft. Most serious winter bags will have at least 8" of loft; a -40F bag will have 10 - 12" of loft. Loft is easy to measure. Put your system together, get a ruler, and measure it from the ground to the top. Temperature ratings matter much less than the amount of loft you have. If you are too big for your inner bag, and compressing the loft, that will adversely effect your comfort rating for the system.

In general, I'd be pretty reluctant to use a 40F bag for a double-bag system unless the inner bag is quite warm. But again, focus on loft, not temperature ratings.