dry down bag?

I think your analysis is correct, it is going to happen, as long as the point where the temp changes from above freezing to freezing is inside the bag – btw it will happen with a synthetic bag too, I read somewhere that the Steger expedition had to start using vb liners because their bags were icing up. So I think the answer is, vb. I hate liners of any sort, never had one that didn’t sort of tangle up in there – have you tried vb clothing? You are nice and warm there in your tipi (I have one too) and before bed you can put on vapor underwear, and whatever clothes on top of that you might want. That answers the other objection to vapor barrier liners, that your clothes get soaked. This way the majority of your insensible persp. will not end up in the down. this might do the trick for you – Others have spoken of using a sythetic overbag, so the freezing will take place in THAT layer, but ultimately it would have to be dried too, wouldnt it. The Steger expedition was using synthetic bags, and they’re the ones who had to go to vb, cause the bags gained about 8 lbs weight from the ice and lost warmth. I have often thought, being out continuously in subzero is a challenging proposition.

a very fast drying synthetic over bag may help. push the dew point out of our down and into the polarguard delta with pertex shell where it can dry very fast in the morning.
this would be my approach on a long trip, although VB may be better and lighter but I can’t imagine more comfy

I’ve slept in the snow and cold quite comfortably with no condensation or ice formation at all when I have used vapor barrier fabric-lined sleeping bags (see Stephenson Warmlite) and the Cocoon inflatable sleeping bag. Have slept both nude and clothed with no moisture problem inside those bags.
Was a terrible problem for the Scott trek to the south pole — they had to break up the ice inside their bags every night to create some insulating loft.

Ice in the insulatoin was also a problem for 1986 Steger Arctic Expedition. IIRC, their sleeping bags weighed 60 pounds at the end of the trip. Took hours each night to warm them up.

His crew used vapor barrier liners on the Trans Antarctic Expedtion with much more comfort.

Comfort being a somewhat relative term in those conditions;-)

I posted this on another thread but couldn’t
figure out how to post a link.—-

Just before Goretex burst on the scene, VBL’s
were more popular as they greatly enhanced the
usefulness of coated fabric rain gear etc. The most
popular undergarment of the time was the large
opening cotton string shirt. This worked really well
as it kept the VBL far from the skin but didn’t
have a lot of fabric for absorbtion. Even better
were the expensive wool versions. I’ve tried polypro
versions but they really pick up oils and smells.
I don’t know where one could get a cotton or
wool version today that doesn’t come with polypro
in it. Maybe Possum down?

One combination I have used with success is a half
bag of silnylon for the legs and waist when sleeping
combined with a VBL jacket. This way your feet
stay warmer than using VBL pants as heat from your legs can more easily reach them. It also can
double as a pack liner.
The jacket can be worn during the day and with the advantage of enabling you to layer coats over the top of the VBL for both sleeping and hiking.
I have found that a VBL jacket over long johns was comfortable with no noticable moisture buildup when hiking in sub zero weather
and balancing my outer layers
to keep from overheating.

Climbers on Denali wear
VBL vests under down gear when climbing to keep
their insulation layers dry next to their backs.

While poking around looking for something else I stumbled on this link,http://www.wiggys.com/legacy/sep-oct00.cfm,it relates directly to moisture accumulation in down bags,partcularily how a 700fill bag will accumulates more moisture then a 400 fill bag. If you have the patience to read through his archives you’ll find a few more references to cold weather sleeping.I just stumbled on this guy,please don’t beat me up.
String net underwear his difficult to find in the US. Devold use to make the wool stuff and brynje is the source of poly,yes,it smells,yes it does seem to work.

The easiest solution for the bag thing is to HANG IT UP as soon as you get up in the morning.

IT REALLY WORKS!

Use your skis or a tree branch. Make sure it doesn’t blow away. Don’t let it fall in the snow. 20 minutes each morning is plenty.

The dampness will evaporate (unless it’s raining). Even if it’s snowing, it still dries out a little.

If it’s cold (below 0c) the moisture will suplimate. It’s slower, but it will still continue to dry.

If you get a sunny morning with a slight wind, take advantage of it!

Maybe your bag will feel a little damp after a few days, especailly near the foot box. If so, don’t worry, you’ll be fine.

I have used a down bag, and camped for 18 days at a time in the Rockies in Wyoming. Sleeping only in snow caves, and the bag stayed dry with out any bivi sack, VB liner or anything. Just a little care in the morning.

perhaps i’m not patient enough to wait. it never seems to be working. i’ll try again.

mike, are you the artist of those cool backpackin’ books? if you are, let me just say that your books are the only outdoor books my wife will read. it is because of the pictures!

Have you tried using the wood stove in the kifaru tipi. It will dry everything out real quick.