Sleeping bags and clothing?

[RokJok]

Originally posted by TLM
Dressing inside a bag is more like using gloves INSIDE mittens, nobody has yet explained how that would lead to MORE heat loss, I would like to see a better explanation.

My guess is that gloves don't lose the heat, they prevent it from being generated in the fingers initially. The physiology of the vasular system reinforces the idea that the extremities (fingers & hands included) are the expendible parts of the body and will be sacrificed if needed to keep the core warm. The blood vessels in the fingers are small, e.g. not built to deliver gross volumes of blood & heat. Thus, anything that restricts the blood flow through the fingers (not a hard thing to do) will seriously impact their ability to stay warm.

To fit the hand at all, the fingers of gloves must be to greater or lesser degree snug each finger. Thus they are squeezing the surface the fingers, which restricts the blood flow. The thicker the insulative layer is built around each finger, the worse this squeezing gets.

With mittens you don't need to maintain any degree of close fit to the surface of the hand, since fine motor skills in mittens are non-existent. When you wrap the fingers in an oversized sheath, you get a lot of that "shared heat" going on between the unconstricted fingers. Camping tip: If you forget (or don't have) mittens you can use plastic (ziploc bags or corners of a garbage bag or plastic grocery bags wrapped around your hand) to fake a pair of mittens.

The advice from Terrill and Nathan to use a hat is some of the best. A polar fleece watch cap weighs only a couple of ounces. But it can make a HUGE difference in how warm you sleep (or hike or stargaze or dash out for the midnight tinkle), especially as the temperature outside your sleeping bag falls past the point at which you can normally sleep comfortably in the bag.

Coyotlviejo, thanks for the tip about using a shirt around the neck as a surrogate shoulder draft tube to block warm air leakage. Now I can stop strangling myself with the pull cord trying to keep that warmth inside the bag.

 

[TLM]

I definitely agree that too tight gloves are cold but that was not the point. The point was that by putting on clothes while in a sleeping bag, that is increasing insulation, you could get colder. I dont buy the idea of one part of body warming another, two body parts at the same temp do not warm each other, there is no heat flow (less heat loss though), if one is colder then it works. Covering your head and even face works well, restricting airflow inside your bag helps (snug bag), having enough insulation underneath helps a lot (most people err here).

Let's make a thought experiment: you start increasing the insulation value of your clothing (inside a bag) so by this theory the better your clothing is the colder you should feel and by the time you reach perfect insulation you (I guess) freeze instantly. Something is not quite right I dont think that the insulation properties of clothing and bag can be separated in the way presented.

TLM

 

[bushblade]

The way I see it is this; clothing doesn't just insulate against cold it insulates against heat too. If you were to get in your sleeping bag wearing your clothes they would prevent heat escaping from your body and heating your sleeping bag ie. you would stay more or less at the same temperature as before you got in. Which is fine for moving around outside, but not the temperature you want to be sleeping at. I say take most of your clothes off, get into your bag, it will be cold for a while but once it does warm up the greater insulation of your bag will keep the heat better.

Excellent tip about wearing a shirt around you neck, makes a good first garment to grab too if you have to exit.

 

[TLM]

A sleeping bag is a heat insulator not a heat source. And usually when you speak of heat, cold kinda follows with it, it's just lack of heat.

TLM

 

[TLM]

After some more thought and some recollections I had a few ideas how clothing in some cases could make you feel colder.

1. You have wet (even little) clothes when you go in the bag, what follows: your heat output after a days walking goes down a lot after you settle down and waters latent heat of evaporation is somewhat large, this does make you colder and the moisture that gets into your bag makes it a worse insulator. If you have a marginal bag this propably would make a cool night altogether. Down's insulating value lowers fast with contained moisture. Better hollow fiber synthetics suffer less.

2. You have dry clothes on but with the bag that's a bit too much and you start to sweat, because there is very little fast evaporation your thermoregulatory system overshoots and you get wet again, what follows is just about the same as previously.

Curiously too warm a bag can also cause you problems. A friend was some years ago testing an arctic rated down bag for a week in some -20C weather. At the end of the trip he was complaining about cold, which should not have happened in a -50C rated bag. We found out that his bag had lumps of ice inside the down. About half a kilo. We figured that he had sweated a lot in that warm bag and because of sub freezing conditions the moisture had collected at the dew point inside the down layer. It had not been a -50C bag anymore. Took a while to dry it.

Wishing everybody warm trips
TLM

 

[coyotlviejo]

Originally posted by TLM
Let's make a thought experiment: you start increasing the insulation value of your clothing (inside a bag) so by this theory the better your clothing is the colder you should

Here's another thought experiment:
You and four other hikers are stranded in a blizzard near the Continental Divide. Help won't arrive for at least 24 hours - if you're lucky. You all maintain 98.6 degrees each, normally. Now, are you all going to crawl into separate sleeping bags to wait out the storm, or are you going to share as much space with each other as possible, maybe even zipping your bags together? And if you all get into one shared and insulated space, are you going to keep your snow suit on to "protect" your heat? That would be rediculous.

Different parts of the body heat at different rates (i.e. the fingers in RokJok's example), so if you can get your hot spots to warm the cold spots, you have maximized the use of your caloric burn.

The fact is that you should have a bag that is built for the conditions you camp in: that's its job. If you have to sleep in your clothes to stay warm you need a new bag.

Another issue is that your clothes are going to get grungy enough without being worn 24-7. Get your clothes filled with body oils and munge and you will lower the insulative value of them and cause them to wear out faster. Let your clothes rest at night, and let your bag take some of the heat - pun intended.

 

[TLM]

If your toes are cold and your armpits are warm I certainly would like to know how you get them to "warm" each other.

Going into the bag with wet clothes on is not a very good idea for several reasons, why would you do it?

If there are no outside heat sources, the only source is your body, the problem is how to minimize heat loss. Joining to bags together does not produce more heat but in most cases minimizes heat losses.

It would be nice if your predictive powers let you accurately forecast the weather, I can't do it so I always cannot match my bag to conditions and I am not going to carry 3 bags just for the fun of it.

It is true that clean clothes work better but what you call body oils are going to get somewhere, your clothes, liner, bag, how is their effect different?

The poor lonely unit of heat escaping from your body has no way of knowing weather the insulation it meets belongs to your clothing or your bag.

TLM