Warmth of combined sleeping bags?

[Joel Barnett]

Is there a way to calculate approximately how warm two sleeping bags will be when combined together?
What I am trying to find out is how low a MH Phantom 15*F regular bag (20oz of fill) combined with a wm's Golite 40*F bag (310g or 10.9oz fill) will get me. I am very thin, so I don't have much trouble fitting inside the two combined bags without compromising their loft.

I would be using this with a POE ether thermo 6 pad combined with a blue CC pad. On my lower I plan on wearing REI thin long underwear with VB pants and fleece pants over that. For my upper i would wear a Patagonia Cap 3 baselayer, VBL jacket w/ hood, thin wool long sleeve over VBL, 100wt. fleece, and a Patagonia down sweater if I am feeling cold. My sleeping footwear would be liner socks, VB socks, and heavy smartwool socks over those. A powerstretch balaclava, vbl & fleece gloves, and fleece beanie round out my head and hand insulation.

What would you take this down to? I am hoping to take this down to at least -5*F. Does this seem feasible or am I hoping for too much?

[Dirk Rabdau]

This gets asked every once in a while – there is a good explanation on the forums here.

Dirk

[Joel Barnett]

Ok, I have taken a look at that article, and I have also read Richard Nisley's CLO chart. The article seems to be somewhat varied in opinions. The formula provided [x -(70 – y)/2 = z] provides this:

X=15 and Y=40: 15-(70-40)/2=0

In Richard Nisley's very informative article, it appears that a a 15 degree bag has approximately 8 clo and a 40 degree bag has approximately 5.25 clo. If you add these together you get 13.25 clo, which is well below the 0* calculated previously. If you extend the chart you get a temperature rating somewhere below -10*.

Now I understand that these charts are approximations and that everyone is different, however, I do know that the Golite is a true 40 degree bag for me, and the MH is at least an 18 degree bag. I also would call myself a slightly cold sleeper, so I doubt that I have a higher MET while sleeping than most. So which way is more accurate?

[James holden]

as a general rule of thumb … add 15-20F for a properly rated summer bag

[David Adair]

A low tech approach: The two bags together have 31 ounces of down. The Western Mountaineering website shows the Lynx has 32 ounces of down and is rated to -10 F. So a rating of 0 to -10F seems like a reasonable guess.

[Joel Barnett]

David, that does seem reasonable. Also, seeing as I will be using VB clothing and wearing numerous layers, I believe I should be comfortable down to -10*. I am also planning to use a silk bag liner. The only issue I am really worried about is my ground insulation.

On a side note, does anyone have any good ways for keeping your breath out of a sleeping bag. I am a side sleeper, and no matter what position I fall asleep in, I always seem to work to my side and, consequently, get condensation from my breath frozen on the outside of my bag.

[Bob Gross]

"On a side note, does anyone have any good ways for keeping your breath out of a sleeping bag."

Crawl into the sleeping bag with your head and neck exposed. Cinch up the drawstring collar around your neck.

–B.G.–

[David Adair]

A little condensation on the outside of the bag is no worry. The worry comes with the subconscious urge to protect your cold nose by tucking it inside the bag. I have done just that and been cold and wet by morning. Big Problem. Some people use a baklava or buff to cover their nose, others cinch up the bag to just a small hole. I use a longer acrylic watch cap pulled down over my face.

You will find what works for you. Personally, I find silk liners are more trouble than they are worth. Same with VB for trips shorter than say 4-5 days. You can air dry your bag and clothes more than you might expect even in cold temps.

I have no experience with your pad set up. A couple CCF pads should be warm enough though.

[Bob Gross]

"Some people use a baklava or buff to cover their nose, others cinch up the bag to just a small hole."

Baklava is a Turkish pastry. Why would you want to cover your nose with a Turkish pastry?

–B.G.–

[David Adair]

LOL Multiple-use, as a nose warmer and you are ready for breakfast.

But I do see your point, a bagel may be a better choice.

[Bob Gross]

A bagel might be a better choice than a turkey.

–B.G.–

[Jim W.]

What is the combined loft of the insulation on top? That basically determines warmth. Using three layers- insulated clothes plus two bags- may be a hassle but it definitely protects against air infiltration or drafts. It sounds like the described system would be quite warm.

To keep my nose and face warm I have found that wearing a mosquito head net adds quite a bit of warmth in moderate conditions without requiring me to snug the hood quite so tight. When it gets to zero F I still pull the strings tight with just my nose poking out.

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