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Where I live in Canada, winter can be pretty cold. Sometimes -35 C. I work outside for a living and among my work peers there's an age old debate about when is the best time to start wearing long underwear (we call them long Johns). Some folks like to stay cozy and start wearing them as soon as the first frost appears. Others believe that if you tough it out in the fall, your body will acclimatize and when it gets really cold, you'll be less cold than your counterparts and won't have to wear as much winter clothing.

Of course, people's body's are different. Some run hot and some run cold. Some have more God-given insulation than others. But do either of these approaches affect your tolerance of extreme cold?

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    My shrewd grandmother would say (I have to translate it from German): "You can do that like Father Assmann. Do you know how he did it? He did it the way he wanted." Oct 20, 2023 at 19:57
  • @Peter-ReinstateMonica: Great saying — what was the original German version? Oct 21, 2023 at 16:44
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    The day's activity surely matters more than any "acclimatization".
    – user17482
    Oct 21, 2023 at 17:28
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    @PeterLeFanuLumsdaine "Das kannst Du machen wie der Pfarrer Assmann. Weißt Du, wie der das machte? Der machte das, wie er wollte." :-) Oct 21, 2023 at 18:40
  • If you perform hard physical work you don't really need any clothes at all when it is -5-10 °C (unless it is windy). Look at Marathon runners running in winter conditions.
    – d-b
    Oct 21, 2023 at 23:10

4 Answers 4

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There is some merit to acclimatisation, but you have to be careful if you're out in the cold for prolonged periods. It's also unclear to what extent you acclimatise in terms of just comfort, and in terms of actually keeping warm (by burning more calories, which might or might not be desirable in its own right).1

Natural insulation is interesting. It insulates your core, but temperature perception is in the skin, outside subcutaneous fat.

Both of these are smaller effects than the difference in people's cold tolerance - not just how much you feel the cold, but how much you mind it when you do. There's also the effect of a water/wind-proof outer layer.

As an example, in your climate, I'd be inclined not to wear long johns above about -10°C if wearing something reasonably warm and windproof on my legs (and good socks) and being reasonably active. But having tested mine down to about -20°C, I'd want more than those if standing around, and by -35°C even if active, I'd want significantly more insulation.

There are 2 things to watch out for:

  • Getting too sweaty cools you fast when you stop exerting. Making this worse, in very cold air breathable stuff isn't all that great, because water condenses on the inside.
  • I would always be sceptical of a "tough it out" attitude. That's how people get hurt, in general. Here, it matters whether you're out for long periods or not. I'll happily go outside for a few minutes in short sleeves down to -5°C, but wouldn't consider it if I wasn't guaranteed to be going back in somewhere warm very soon

1 Seasonal acclimatization to cold in man, Thomas R. A. Davis and D. R. Johnston, Journal of Applied Physiology, Vol. 16, No. 2, Mar. 1961 suggests both factors are relevant, with a reduction in preferred temperature of 5°F (approximately 3°C), and a small reduction in heat generation but a larger reduction in shivering.

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    Is there any evidence that acclimatization to lower temperatures really works? What would be the physiological mechanism that enables us to stay functional in colder weather than before? (Apart from accumulating a layer of body fat which I tend to do in the warmth of my home under the Christmas tree, in preparation for the upcoming extreme hikes, or so I tell myself ;-).) Oct 22, 2023 at 4:30
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    @Peter - Reinstate Monica There seems to be some evidence for this: Thomas R. A. Davis and D. R. Johnston, "Seasonal acclimatization to cold in man", Journal of Applied Physiology, Vol. 16, No. 2, Mar. 1961, pp. 231-234: "The highly significant change in shivering and the less significant change in heat production observed suggests that man seasonally acclimatizes to cold and that this acquired acclimatization is lost during the summer months."
    – njuffa
    Oct 22, 2023 at 9:29
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    Thanks @njuffa, I've been offline for a couple of days (kayaking, mountain biking, and van camping, so good on-topic reasons!). The literature I'm more familiar with is about acclimatisation to cold water immersion, but there's some overlap in my reading.
    – Chris H
    Oct 22, 2023 at 20:04
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    @Peter-ReinstateMonica one interesting possibility is changes in brown fat, which generates heat. In general human metabolism is very adaptable, but cold tolerance goes beyond metabolism
    – Chris H
    Oct 22, 2023 at 20:08
  • @njuffa - does that paper say that acclimatization to cold is - you get a little warmer but essentially you just stop shivering?
    – D Duck
    Oct 23, 2023 at 6:52
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I personally would take the safer perspective, and start wearing long underwear earlier than others, and adjust my outer layers as necessary. Long underwear is functionally little more than tight fitting sweat pants, just another layer to wear beneath your outer layers. Since outer layers are easier to change out of or into, I would focus on changing those rather than having to strip to change my protection from weather.

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  • I would hope that an outdoor base layer for the legs doesn't soak up water (sweat, melted snow that snuck in, etc.) like sweat pants. Certainly mine don't, apart from one very old pair that I never use.
    – Chris H
    Oct 28, 2023 at 20:46
  • @ChrisH I didn't mean one should substitute sweat pant for proper long underwear, though it can work in a pinch if your pants are baggy enough. The point is it's another warm layer that goes on the inside and nothing more than that.
    – Escoce
    Nov 2, 2023 at 17:37
  • Ok, I took "functionally equivalent" too literally - but that's because one function of a decent base layer is to wick away sweat.
    – Chris H
    Nov 2, 2023 at 20:36
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I am more sensitive to cold than the average person, in fact more sensitive than anyone I know. I have very little natural insulation.

On the specific point about acclimitization: people vary a great deal on how quickly and how well they acclimitate. For example I would never, never, never acclimitate to -35 C to the point where I would not need an underlayer.

I find a single layer not enough at about zero degrees C, particularly when it is windy. However, as a woman, I have an option that might be too far out of the envelope for most men: nylon panty hose. They are remarkably warm, extremely light, quickly and easily washed, and dry quickly. Long johns -- sweaty, dirty, a pain to wash, ugh.

I have been comfortable hiking at -15 C with the panty hose layer under fleece pants. Just pretend you are buying them for your overweight great aunt; you will find something that fits.

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    For the person stating being more sensitive to cold than anyone else, so am I. If you haven't already, have your thyroid checked. It could, as is mine, be hypothyroidism. There is medication for it.
    – Keky
    Oct 21, 2023 at 17:54
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    @Keky It wasn't hypothyroidism. But point is well taken. A small, inexpensive pill, synthroid, fixes hypothyroidism
    – ab2
    Oct 21, 2023 at 20:13
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    Leg length is likely to be an issue for some of us men but they're probably available if you're prepared to look in the right places. A rather thicker option that also works if you want something close fitting is cycling tights. Cheap ones without much padding are better off the bike than gel-padded. Nylons under fleece probably adds up to about the same insulation as warm bike tights or light synthetic long johns under the heavier sort of hiking trousers
    – Chris H
    Oct 28, 2023 at 20:43
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    @Chris H Valid Point! I was 5'10.5" when I started wearing pantyhose (although I am 1.5 inches shorter now). That was when that was tall, even for men. Nylon hose stretches. But I agree that a 6'4" man might have trouble finding a fit. Although....one of my female second cousins is 6'2" (slim, gorgeous and a competitive volley ball player.)
    – ab2
    Oct 29, 2023 at 19:56
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    I should have prominently added that my 6'2" female second cousin, slim, gorgeous and a competitive athlete, is also very, very smart. Sexual stereotypes become reflexes even in those of us who have defied such stereotypes for decades in our own lives. (This comment IS pertinent to TGO; would be glad to politely debate the point with someone who disagrees.)
    – ab2
    Oct 29, 2023 at 20:05
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You probably own more than one long johns right? You might notice that they're not all the same warmness. Early in the winter, you can wear the ones with less insulation on colder days and regular underwear on warmer days. As the winter progresses, you use the thicker johns for the coldest days and thinner one for the less cold days. As the winter subsides, go the opposite way.

Combine this with varying thickness level of your outer pants, upper base layers and upper wear, so that you get a more constant body temperature throughout the year.

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