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?