How cold does it have to be before "bundling up" does no good and you still freeze to death?

Suppose you put on two sweaters and a decent winter coat, how cold does it have to be before it overcomes your trapped body heat?
Make whatever assumptions you want about the size or BMI of the individual, or the quality of the coat, or the phase of the moon, or whatever else you want.

I don’t know, but it is colder than the mid-teens (F°.) I handle that fine.

To go to a ridiculous extreme- Rated for -40F
$810-840
https://www.rei.com/product/881351/marmot-cwm-sleeping-bag

If I get to make any assumptions I want, there is no temperature that will “overcome my trapped body heat”.

Another layer will always slow down heat loss and all you have to do is keep the heat loss below your natural heat production. Before that becomes truly impractical you will have reached the point where the air is so cold you need breathing apparatus to avoid instant frost bite in your air ways.

I walked around in Rangely Colorado in winter of 80-81 when it spent a lot of time on the shivery side of -20. Two shirts, two sweaters, a down jacket, long johns over regular undies, jeans, wool socks, gloves, wooly hat, scarf, winter boots. I slept in an unheated shack then, too. Wrap all that minus the boots in a serious down sleeping bag.

All this is not to say that there’s no temp you can’t simply dress for. I suspect the limiting factor is your lungs, and how cold the air can be before you can’t breathe it. (would not be doing the lining of your mouth and nose, not to mention your eyeballs, a lot of good either at that point). But based on photos of Arctic and Antarctic explorers, and Siberian and Alaskan and Canadian folks, I assume our planet doesn’t do those kinds of extremes on a regular basis.

There are many factors to consider beyond how much you bundle up, including how much heat and moisture your body is generating.

In the winter I’ll run with nothing more than a tee shirt and running pants over a moisture wicking layer covering everything except my head (not counting shoes, socks, hat, ear muffs, etc). Running at 20F or warmer is more or less comfortable. Below 20F I can still do it but it’s fairly miserable. I’ve not tried below 0F.

The most important things in this case are managing moisture and not stopping. As long as I never stop running I’m pretty safe but I have gotten some minor frostbite when I let my clothes get too wet.

We’ve made clothing/suits well enough insulated to allow astronauts to survive the cold of space, so i don’t think you’ll find a temperature too cold to dress against. Of course, you can start adding conditions such as whether the person is active or stationary, how fancy the insulating technology can be (helmets/self contained air source, supplemental heat), and how long the person has to be out which can change the answer. But if natives in the Arctic could survive with just furs and hides for generations, I don’t really think it gets so cold it won’t matter.

If I may inject a semi-hijacking question into the thread: If warmth is all about the insulation provided by trapped air, and not necessarily the thickness of the clothes, does this mean that someone could wear something ludicrous like ‘clothing’ made out of 20 trash bags (20 layers trapping air in between each) and be warm at the South Pole?

This.

It can’t get infinitely cold. On Earth’s surface the lowest temperatures are nearly half way down to zero, relative to the highest temperatures. We already dress sufficiently to handle that. Clothes to handle absolute zero wouldn’t be too unworkably bulky, especially with modern materials.

Even if you bring wind into it, a single layer of trash bag completely stops wind. Now if wind or floods or other things rip your clothes off, it’s a different situation. But broadly speaking clothing technology is more than able to take you as cold as it’s possible to go.

Generally speaking, the problem of keeping an astronaut at a living temperature in space is more about keeping them from overheating than from freezing. The common notion that “space is cold” isn’t really correct; while the background temperature of interstellar space is about 2.73 Kelvin (-270.42 ℃, -454.75 ℉) there is no medium (e.g. an atmosphere) to transfer away thermal energy via convection the way there is on Earth. Therefore, the only way to reject heat is via radiation, which isn’t really that high at human body temperature (about 37 ℃) and pretty easy to stop simply by using ainsulating barriers and non-emissive materials. However, at Earth orbit the effective temperature on a sun-facing surface is about 393 Kelvin (120 ℃, 248 ℉), which is hot enough to roast an astronaut quickly. This requires both a reflective outer suit (hence, why both NASA and Russian EVA suits are white) and an active cooling garment that circulates cool water to keep the astronaut at a comfortable temperature as well as an insulating undergarment.

Warmth isn’t just about trapped air; while the air near the skin or base layer helps to both keep the user warm and carry away moisture, there also needs to be insulating layers between this air and the outside or it will cool quickly. If you’ve ever used a wetsuit the principle is similar; by getting water trapped between the highly insulating neoprene outersuit and the skin or chafeguard, this keeps the diver warmer than they would be if the suit were sealed from water, as the inner water acts as a thermal mass. If you dive in a drysuit, you have to wear additional fleece insulating garments to stay warm (but the advantage is that you get to stay dry, so once you get out of the water and strip off the suit you aren’t suddenly freezing in the air).

The coldest sleeping back rating I can find is -40 ℉ (which as it happens is also -40 ℃). Given that a sleeping bag is basically the best case for maintaining warmth (no separation between limbs, no openings except the hood, et cetera) that is probably a good estimate for the indefinitely sustainable lower limit without some kind of active thermal garment. At that temperature unprotected skin will experience frostbite in under 10 minutes so every part of the body including face, eyes, and hands would have to be covered with insulating protection. Although people have certainly experienced temperature of down to -90 ℃ (-130 ℉) people can generally only withstand such temperatures for a limited interval of time without additional protection in the form of a heated structure or other active warming.

Stranger

I think the problem is that your 20 trash bag ski jacket isn’t sealed air-tight and a significant portion of each layer of plastic will touch the next layer. So cold air is going to seep in between the layers and heat is going to transfer through where the plastic touches plastic.

But I mean, based on people going to the top of Everest and the Antarctic, I don’t think there is a place on Earth so naturally cold one can’t “bundle up” for.

This, right?

Furs and hides are good, but the downside is that they can be heavy. You get used to it, but there is a certain encumbrance.

Also, the arctic natives used to use animal intestines to make a waterproof layer. This one is made from seal innards:

Couldn’t you just take whatever the sleeping bag is made out of and make three more, each bigger than the last, and quadruple your thermal insulation?

The reason there aren’t sleeping bags rated below -40 probably has more to do with the fact that there’s no market for sleeping at lower temperatures than absolute survivability.

Counterpoint: something like 6% of people who attempt the Everest summit die, and I bet the cold has something to do with it. No one stays at the Everest summit for very long, although arguably that has more to do with oxygen than temperature.

Arctic natives survive with natural materials, but also

  1. Sometimes they didn’t
  2. They had structures.

I’m assuming by “bundling up” we’re counting clothes, not buildings. If you count insulating buildings then I bet you can survive down to whatever the freezing point of oxygen is.

You can but there is going to be a limit to how effective that is. What the insulation layer is doing is slowing the rate of heat transfer from the interior to the outside, creating what is hopefully a sharp gradient. As you add more bags (which are going to have to be progressively larger like matryoshka dolls) you are creating a less sharp gradient but you are actually adding thermal mass that is going to absorb energy from you. Eventually the outer layers are going to be just as cold all the way through as the outside and won’t do anything to increase the gradient.

One thing that expedititioners and mountaineers sometimes do to extend the rating of the back is to put a vapor barrier inside the bag, preventing moisture from your body from escaping and taking thermal energy with it. Essentially, it creates a sauna powered by body heat. The problem, however, is that you can end up getting really clammy and when you crawl out the moisture freezes on you. I’ve had this happen and it is not fun to say the least.

The o.p. asked about the limiting temperature for someone wearing clothing (“two sweaters and a decent winter coat”) and that is obviously going to be less effective than a sleeping bag even of the same nominal insulation value because there will be more openings and separation of the limbs from the torso. You can put on more clothes (my record is six layers; a next-to-skin wicking base, a second heavier ‘base’, a light internal wool/fleece layer, a middle heavy sweater layer, a parka or down jacket, and then an anorak as a final windbreak) but at some point in the layering process you are going to have so many layers on that you will lack the necessary mobility to do anything useful.

Temperatures can certainly get dangerously frigid on Mount Everest and other “Eight K” mountains and you can suffer a disabling frostbite injury that leaves you unable to descent to base camp, but the conditions that really get most people are high altitude pulmonary edema (HAPE), high altitude cerebral edema (HACE), and just plain exhaustion from the lack of oxygen and poor conditioning or preparation. Everest is not all that challenging from a technical standpoint–the only equipment needed for the southeast ridge route need beyond protective equipment is a basic ice axe and supplemental oxygen (along with the preplaced ladders and ropes that are set up at the beginning of every seasons)–but the conditions on the ascent from base camp is really at the limit of what humans can tolerate, and many people find that they cannot.

The indigenous populations living above the Arctic Circle have a number of practices and adaptations so survive in the harsh winter conditions. For one, as you note, they build robust structures. Snow is an extremely good insulator and makes a great construction material up the the point that it melts. They also hunt animals for their fur; seals in particular have very insulating coats and are easily as good as modern down clothing for their weight, and unlike down are also essentially impermeable to water. They eat a very fat-rich diet and have physiological adaptations that allow them to tolerate arctic conditions better than non-natives.

And, as you point out, sometimes they didn’t survive. There are only oral traditions so we can only guess at mortality rates of pre-contact indigenous populations of the Arctic but their traditional lore includes a lot of death legends with creatures like the Qalupalik, which are clearly metaphorical cautionary tales about the dangers of being incautious about falling into water.

Stranger

Wow, I wonder how much they paid the people who participated in that study! they slept in the cold with their head in a box (to measure how much oxygen they used) and a rectal thermometer and skin thermometer. That sounds really unpleasant.

Your body heat can be used to warm the air before you inhale it. That is like heat lost though. You need to exchange air also to get rid of the air you exhale, so without something like a respirator that separates inhalation and exhalation you’ll have higher losses to keep CO2 from building up.

Conceivably you could use a closed breathing system that captures exhaled CO2 and minimizes external air intake, or even uses it’s own oxygen supply. Getting into some pretty cumbersome clothing at that point.

Everest Schmeverest. That’s a scant 29000 feet high. In 1961, Paul Bikle flew his glider to a world-record altitude of 46000+ feet near Lancaster, Ca. His son had that glider on display in a hangar at Hollister Airport, Ca., for many years, along with a newspaper article describing how he dressed for the occasion. I don’t remember the details, but he did manage to bundle up for it.

Yeah, at this point you are kind of getting to the point of “bundling up” by wearing a space suit.

Heh, back in the late 80s I was paid $300 a night as a normal control in sleep studies, and it just involved sleeping. Sure, there were EKG and EEG electrodes glued to me, but no pain. When the study involved nocturnal penile tumescence I got a $50 bump.

At that same time there were studies involving moderate discomfort that paid $10. I turned those down.