🚀 go-pugleaf

In message <7uv4qngmy5r.fsf@ipana.research.nokia.com>, MB <*@*.*> writes
>Chris Townsend >
>> And black is currently very popular - most soft shell clothing seems
>> to be black.
>
>That sucks <g>
>
>> I can't say though that I've really noticed the difference
>> between pale and dark coloured clothing in terms of warmth.
>
>I guess Chris means in winter.

Yes.

>Being cold or warm
>depends on so many factors that it's difficult
>to notice the relatively minor effect of exterior colour.
>However, if you check with a thermal imager, you'll notice
>a marked difference. Silvery stuff, such as those mylar
>bags, is actually pretty good at stopping radiative
>heat loss due to the very low emissivity of the
>material. Mylar is good as thermal camo too, btw, when
>you really don't want those SAR people to find you... ;)

I don't think heat loss is significant though. Any tightly woven 
clothing will prevent most of it. Convection, conduction and evaporation 
are far more important and with these colour is irrelevant.
>
>In summer, in sunshine, the difference in "hotness"
>of black vs white is so obvious that I'm sure everyone
>is familiar with it. It's easy to notice when wearing
>eg woodland camo: the black spots feel much more hot
>than the dark green and brown ones and the light green
>is even less hot.

True, but do you feel hotter inside at those spots? I've tried black 
T-shirts in hot weather and although the fabric feels hotter than a 
white one I don't feel noticeably warmer.
>
>> I suspect "technical" clothing doesn't come in white or
>> silver often because it shows the dirt.
>
>This, of course, is yet another reason why it should be
>white or silver. It's useful that the dirt shows. Dirt
>typically degrades performance (like breathability or
>insulation) and if the dirt shows clearly, it's easier
>to judge when the stuff needs to get washed.

True again, but pale clothing can look grubby in a few hours.
>
>> I like black sleeping bags - they absorb heat and dry fast
>> when damp.
>
>Sure. But only if you have a significant source of thermal
>radiation visible, like sunshine or fire. In midwinter
>cold-camping (eg above treeline or environmental policy)
>you have neither. And, that's presicely when bag warmth
>really matters. Moreover, you should be using a VB liner
>in such conditions, and thus, hopefully, have much less
>need for drying the insulation of the bag.

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.

Now it maybe that on a much longer trip there would be problems with 
condensation. I wouldn't fancy a longer trip in such cold conditions 
anyway :-).
>
>Agreeably, radiative heat loss isn't that much of an
>issue with bags, as one usually uses the bag inside
>a confined space, like a tent. Moreover, if
>the bag is warm enough, it's exterior temperature
>is close to ambient, which again reduces the
>relevance of the emissivity. Otoh, if you'll forced
>to use the bag without a shelter or cover, and the
>bag isn't warm enough, it's exactly the conditions
>where the radiative loss is biggest. And, also, it's
>the conditions where you could do without any extra
>heat loss... (These are qualitative comments though,
>one would have to do calculations and measurements in
>order to check the relevance of the quantitative
>difference.)

I think if you're forced to use the bag without shelter or cover you 
have problems anyway :-). Of course bags with waterproof or water 
resistant covers have built-in protection.
>
>Nevertheless, I agree that it's mostful if the bag
>is black with open fire or sunshine available. Imo,
>however, it's sufficient that the _inside_ of the
>bag is black, as it's typically turned inside out
>for drying.

Agreed that only the inner or outer needs to be black. I prefer it to be 
the outside as I find light coloured inners more "friendly".

> I'd like a winter bag to be silver or
>white (added benefit of being visual camo too) on
>the outside and black on the inside. The only winter
>bag that comes to mind with silver colour is
>Stephenson's Warmlite Triple, the VB of which
>is silver coloured on the _inside_ of the tops. As
>far as I can see, silver on the inside isn't very
>useful - it's actually just the exterior colour that
>matters - ie the emissivity of the outermost layer
>wherefrom the thermal radiation escapes into cold
>space (see eg Glen Randall's 'Cold Comfort').

Silver inside certainly doesn't seem to make any difference. I've tried 
bags with silver linings and with sheets of silver foil in between 
layers of insulation and I don't think they make any difference, except 
that the foil makes the bag less breathable.

Winter for me usually means high winds, wet snow and rain and 
temperatures around 25-35F. I use a three season down bag, currently one 
with a mid blue shell and a grey lining, and a tent. If using a snow 
shelter I use a breathable bivi bag. My red/purple winter bag (rated to 
-15F) is too cold for home conditions though I will take it on a Nepal 
trip this autumn where temperatures could be as low as -15.
>
>Otoh, silverized insides of shelters is useful,
>especially in case of tarps used with a fire in
>front. Acts as a thermal mirror.

Good in the desert too. I found that a space blanket kept me cooler with 
the silver side facing the sun than facing me when used as a sun shade.
>
>Oh well, I seem to have got carried away...

It's an interesting discussion.

And a long way from hiking in skirts :-)