As a long time avid outdoorsman and engineer, I’ve done all the layering, different materials, “if your feet are cold put on a hat” type advice to stay warm. Mostly it works, but is it optimal?
Something occurred to me last camping trip - don’t you really want your thick insulating layer (coat) to be snug fitting rather than loose?
Reasoning: Outside air is cold, body is warm. The air near the body gets warmed, but is also convecting and being pumped out from under the coat with motion and replaced by (usually) cooler air. So while the coat protects the warm air from the cold air by insulating against heat transfer, with a tighter fit of the same coat less air transfer occurs.
But air is a decent insulator too, some of our best insulators (e.g., styrene foam) work by essentially just mechanically trapping air using chemical wizardry. So it’s not obvious whether you want a big air gap or small…
Anecdotal observations: Went camping last week with some friends in freezing weather, one of which had snug clothes and was tolerably warm, while the other two guys (Greg and I) were wearing pretty loose stuff, and mostly freezing.
Also, when cold in a blanket it seems like snugging it up against your body helps stay warmer than leaving it all loose and raggedy.
Obviously being cold is sub-optimal so I want to avoid it whenever possible…
So what say the dopers on this basic subject of keeping warm?
It depends on the coats. In particular, how windproof the outer surface of the coat is which leads to lots of heat loss. The more windproof your coat the bigger an air pocket you can maintain (assuming your body is producing heat at a normal rate). But very loose fitting coats will allow air exchange at the bottom so you can clearly go too big.
Well, a big pocket of air isn’t all that insulating since the air moves around within the pocket, transferring heat. What you want is lots of tiny pockets of air trapped inside insulation, so the air can’t move.
And then if there’s a big pocket of air in your coat, it’s more likely to get pushed out the sleeves or waist or neck when you move.
So I think the optimum for a coat is
a) large enough that it’s not squeezing any insulation layers;
b) snug enough overall and particularly at the edges so that warm air doesn’t escape when you move around.
Based on the ‘soft cooler’ theory, a soft sided cooler that you compress around the contents is better than a hard sided one with lots of air space, then snug makes more sense. And as pointed out above lots of air will escape unless you have some kind of loose coat I’ve never heard of.
If you have ribbed wrists on the sleeves so they fit snug, a drawstring around your waist and a turtleneck at the top, you can trap a good amount of air inside the coat. A high enough level of activity is going to force the air in and out no matter what, though, so if you’re going skiing or chopping firewood you probably want multiple, closer layers.
Based on our winter survival training course - you want some air, but not a big pocket. In short, too loose is not good and too tight is not good. You are correct that you need some air to provide insulation and warmth. And alyers are better than one giant coat.
You don’t want to sweat. You don’t want to be freezing. I have run in up to -50 and it’s fine with two “tech” layers and a windproof outer, as long as my exposed skin was covered and I was running.
