What actually keeps you warm outside

Start with the thing almost everybody has been told, because it is wrong and because believing it changes what you put on.

You do not lose most of your body heat through your head. It is not 90%, it is not 50%, and the head is not a special radiator. That figure has an origin, and the origin explains everything: it comes from studying people dressed in Arctic survival suits, with nothing exposed but their heads. Cover all of somebody except their head, and yes, most of the heat leaves through the head. That is a fact about the suit.

Which does not mean go bare-headed. An uncovered head loses heat the same way any other uncovered part does, and a hat is cheap. It means something narrower and more useful: if you are cold and choosing between a hat and a coat, the coat wins. People were emphatic about that, because the myth gets it backwards.

What keeps you warm is several thin layers of anything except cotton, loose enough that your blood can move, with something windproof on the outside.

The thing you were told, and the thing that matters instead

Cotton is the problem, and it is the one change that does most.

Cotton holds water — your sweat, rain, snow that melted on you — and then it stays wet, and wet fabric against skin pulls heat out of you faster than bare skin would. It does not dry while you are wearing it. Jeans are cotton. Most cheap socks are cotton. Most T-shirts under a coat are cotton.

Wool or synthetic instead, particularly for the layer touching you and for socks. Both keep insulating when damp, which is the entire difference. This matters more than the coat does, and it is why someone in a good jacket and a cotton shirt can be colder than someone in a cheap jacket and a wool base layer.

Cover your ears and your hands and your feet, for the ordinary reason that they are exposed and small. Mittens beat gloves when it is really cold, because your fingers warm each other instead of each being alone in its own tube.

Why thin layers beat a thick coat

The warmth is not in the fabric. It is in the still air the fabric holds, and several thin layers trap more pockets of air than one thick one does.

Layers also let you adjust, and adjusting is the actual skill. Which brings the part people were most insistent about: do not let yourself sweat. Sweating in the cold is not a sign you are winning. It wets the layer next to your skin, and a wet layer is the thing that makes people dangerously cold on the way home. If you feel yourself getting hot on the walk, take something off before you are damp, not after.

The outer layer has a different job from the ones underneath. It is not there to be warm — it is there to stop wind stripping away the warm air your other layers are holding. A windproof shell over thin layers beats a thick fleece with the wind going through it, and it is why a cheap nylon outer can transform a set of clothes you already own.

The mistake that feels like the solution

Here is the counterintuitive one, and it is the reason a lot of people conclude their feet are simply cold people’s feet.

If clothing is tight, it makes you colder. Blood is what warms your hands and feet, and anything that squeezes — tight boots, thick socks crammed into boots that already fit, a glove that pinches — restricts the blood getting there. You end up with more insulation and less heat.

So the answer to cold feet is very often fewer or thinner socks rather than more, or a bigger boot. If your foot is being compressed, another sock makes it worse. People who skate or wear fitted work boots kept running into this, and it took them a while to believe it.

If you are standing still

Moving keeps you warm; standing does not, and standing on concrete or asphalt is worse than standing on almost anything else. Cold ground pulls heat straight out of your feet by contact, continuously, no matter how good the boot is.

Anything between you and the ground helps — a rubber mat, a scrap of foam, a folded piece of cardboard. One person doing outdoor work described it as the single change that made a shift bearable, and it costs nothing.

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One last thing, because it is the reader this page cannot help.

If the problem is not a walk to work but a flat that will not get warm, none of the above reaches it. Layering is for a body moving through cold air; it does not answer a cold home, and the honest answer to a cold home is a different one about insulation, draughts and what help exists for heating bills.

What this page can do for that reader is one warning, because it is what people reach for: be careful with open flame. Candles and portable stoves used for warmth are how house fires start, particularly near curtains, bedding, or an animal that will knock something over. If it has got to that, the thing worth spending an hour on is finding out what assistance exists where you live — that is a better use of the evening than trying to heat a room with a naked flame.