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I'm not a big guy, but I can sit in a cold pool of still water for a long time if I stay still and control my breathing, my skin gets cold, but after you get past the cold shock I can sit there rather comfortably without any signs of my core temperature dropping (shivering, etc.). One of my favourite things to do is sit up to my neck in the cold spring pool (4°C) at Ainsworth Hot Springs for about a half hour at a time and watch the shocked expressions on peoples faces as they dip their toes in the water, or try to take a quick dip, then look at me in bewilderment as I sit there seemingly unfazed by the temperature.

When we were kids we used to tube down the Elk River in BC, which is fed by a glacier lake. I have one sibling who was quite a bit thicker than the rest, and while the rest of us tried our best to stay on top of our tubes and out of the cold water, they would just float in a life jacket with the current, without any signs of really getting cold aside from hands and feet.

I've been pondering this lately, wondering how much having a good layer of fat on you can help insulate against the cold. There are a plethora of animals in nature who rely on a thick layer of blubber for insulation; narwhals, beluga whales, walruses and many others for example who don't also have fur. Fat obviously won't protect you from frostbite, your skin can still freeze, but I wonder if it might help prevent advanced stages of frostbite (freezing down to the deep tissues like muscles, tendons and bone). Or how about hypothermia? Are obese people less likely to become hypothermic? One thing I was considering was in the case of severe exposure, where frostbite and freezing are a serious danger. Would a large person have better chances of survival if they were to submerge themselves in water? Liquid fresh water is typically always warmer than than zero in nature, if it was 20 or 30 degrees below zero, could a person with a thick adipose layer survive the cold and protect themselves against frostbite by sitting up to their neck in a pool of still water? Would their fatty layer help insulate their core like a layer of blubber?

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    I anticipate this question may offend a couple of people. It's not intended to, I'm legitimately curious. – ShemSeger Jan 4 '16 at 5:11
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    Adding as a comment as it is based on a tv show and it isn't directly to do with water. Brainiac: Science Abuse used to do tests like this. Someone underweight vs someone overweight. In the test they sat in a cold room maintained at 0°c. After 25 minutes the tests was stopped. The underweight person's core body temperature had dropped by more than 3°c. The overweight only 0.6°c. – Dynadin Jan 4 '16 at 7:18
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    @Dynadin That could simply be because of mass. You could conduct the same test with two different sized buckets of water and the results would be the same. So in general a larger person will stay warmer longer, but do they need as much extra insulation to maintain their body temperature? – ShemSeger Sep 16 '16 at 1:49
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In humans not a lot. There are significant differences between blubber and fat. Though blubber is mostly made of fat it has very different composition to human fat. An animal with blubber also uses it in very different ways to the way a human uses fat. Fat in a human is an energy source, not insulation:

(blubber)... can comprise up to 50% of the body mass of some marine mammals during some points in their lives, and can range from 2 inches (5 cm) thick in dolphins and smaller whales, to more than 12 inches (30 cm) thick in some bigger whales, such as right and bowhead whales. However, this is not indicative of larger whales' ability to retain heat better, as the thickness of a whale's blubber does not significantly affect heat loss. More indicative of a whale's ability to retain heat is the water and lipid concentration in blubber, as water reduces heat-retaining capacities, and lipid increases them.[2]

Wikipedia

Blubber is also rich in blood vessels (which the fat of a human isn't), these blood vessels adapt to temperature, this allows the animal(s) that have it to react to changes in temperature. So a whale, for example, can "re-route" blood to underneath the blubber when cold. In humans the blood is outside of the fat layer (on the skin). A constant supply of blood is required prevent frost bite (the skin dying).

Marine mammals have other adaptations too, the have a relatively low surface area to mass (when compared to say a human). So they can retain their heat more efficiently in their large bodies. Humans have a large surface area to body mass. We're adapted to life in much warmer climates, having evolved originally in Africa.

If it's really cold they also migrate into warmer waters, nursing mother wales do this.

A bigger factor in influencing humans in extreme cold is how their body reacts when it drops below the ideal 37.5C temperature. Below this temperature human organs begin to shut down, vital ones like the brain, heart, liver, etc. When this happens it's called Hypothermia. A body temperature between 32C and 35C is mild hyperthermia. Below this is life threatening.

An interesting case study is Guðlaugur Friðþórsson (an Icelandic fisherman involved in a ship wreck in the arctic ocean). He survived 6 hours in 5C water. When he got to land his core body temperature was 34C yet he showed limited signs of hypothermia. No one really understands how this process works as it's very rare but it appears some people have an ability to protect their vital organs even when their core body temperature drops below what would kill 99% of humans. Though overweight it was decided that this had a limited impact on his survival and it was his natural (unexplained) adaptations that saved him. They made a film about it The Deep/Djúpið

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