🚀 go-pugleaf

Chris >
> True again, but pale clothing can look grubby in a few hours.

Sure, but that's because it has such a wide range of dirt
indication. It takes quite a while before it's as dark as
something that's dark to start with. :)

> I've tried VB liners and I have to say I don't find them
> comfortable. The longest trip I've done in really cold weather
> (overnight lows -5 to -12F) lasted 13 days. I used a down bag with a
> water resistant shell. It had a red outer and a dark purple inner. I
> didn't use a VB liner. I aired the bag most days (some were too
> stormy) and it stayed dry. Although there was little heat in the sun
> (and most days it was cloudy or hazy anyway) there was a breeze and
> the air was dry, which is why I think any moisture in the bag soon
> evaporated.

In my experience, keeping a bag dry in mid-winter (northern 
Finland and some NW Russia) without VB in cold-camp on 
several consequtive nights simply doesn't work. 13 nights 
sure is well beyond that. Otoh, in spring winter, even in 
relatively cold weather, keeping the bag dry usually seems 
trivial by comparision... long days, often with sunshine, 
vs polar night with a few hours of twilight.

Airing out humid warm air of a relatively warm sleeping 
bag before the bag cools and the moisture starts to condense,
works, of course. But, if the ambient temperature is low, and 
the bag has sufficient insulation, there will be a large 
temperature gradient through the bag insulation, and 
the exterior parts never have a chance to warm. Without 
VBL, evaporative transpiration will then condense and
accumulate frost within the cold bag insulation. 

Note that the tent interior may be significantly warmer 
than ambient, which improves the chanses of drying the
bag by airing it. Also, more of the evaporative transpiration
will then get through the bag and condense on the cold 
interior walls of the tent rather than inside the bag
insulation. Getting the tent warm enough for this 
typically requires some form of heating, a stove or such.

If outer parts of the bag insulation remain cold after 
the night, and there's condense and even frost inside, 
there's no way one can simply air it away. After all, 
there's snow in the surroundings too, and that doesn't 
get aired away either...

Sunshine absorbed in the (preferably) black (interior) 
fabric will of course warm the bag, evaporating some 
moisture, and also result in a vapour pressure pushing 
moisture through the bag and out of it.

In midwinter, at high latitude, the Sun won't rise, so 
waiting for sunshine to dry the bag isn't really practical
:). Moreover, very cold weather in the Arctic is typically 
associated with windstill, so airing is the least efficient 
when it'd be needed most. And, wind is typically associated
with low-pressure fronts, and that means it tends to be
snowing or raining sleet or whatever.

Typically, in midwinter, the relatively few people 
who backpack over here (Fin), seldom use cold shelters 
for more than occasional single nights. By far, most 
nights tend to get spent in the warmth of wilderness 
cabins. Some may use tarps with live fires, fortunately 
the all-night buring traditional log fires are rarely used 
nowadays (lots of impact). In this light, it's perhaps not
so surprizing that sleeping bag VBL's used to be practically 
unknown over here. 

But, imo, VBL is the way to go, if one is to cold-camp in 
midwinter cold conditions on consequtive nights. The slight 
uncomfort of VBL is a low price for retaining the insulative 
loft of one's bag.