Why a wet layer pulls heat out of the skin

Short answer: Water conducts heat far better than air, so a wet layer draws heat away from the skin many times faster than a dry one. At the same time, evaporation cools you further. That is why you get cold quickly in a soaked layer, even when it is not cold out.

Water conducts heat well

Water conducts heat around twenty five times better than still air. A dry layer holds a thin cushion of air against the skin, and that air slows heat loss. When the layer gets wet, water replaces the air and the insulation disappears. That is why a soaked layer feels cold even in a warm room, including a bamboo sweatshirt for women.

Evaporation takes energy

For water to evaporate it needs heat, and that heat comes from your skin. Every gram of water leaving the fabric takes a little energy with it. That is why a damp layer cools you more than a dry one, even in still air. You notice it clearly in a close fitting layer like a bamboo bra that is damp after a long day.

Two effects at once

A wet layer cools you in two ways at the same time. The water conducts heat straight away, and evaporation takes even more with it. Each effect is noticeable on its own, but together they make the body lose heat fast. That explains why you can feel cold after a walk in mild weather simply because your clothes got damp.

Wind makes it worse

In still air you get cold within minutes, but in wind it happens much faster. The wind removes the damp air just above the fabric, so dry air takes its place and evaporation speeds up. At the same time, the little still air that was left gets blown away. A wet layer in the wind is one of the coldest things you can wear.

What to do about it

Change into a dry layer after you have been sweating instead of waiting for the fabric to dry on you. Or choose a material that moves moisture onwards so the skin is not lying against water. Bring a spare set if you know you will get warm along the way. The same goes for bamboo socks for men and women.

Feet get forgotten

Feet sweat a lot, and socks are shut inside the shoe where moisture struggles to escape. Wet socks make your feet cold even when the rest of your body is warm. If you have been on your feet for a long time, it is worth changing into a dry pair. It is a small thing, but it makes a clear difference to how your whole body feels.

A layer on top can help

A layer over the damp layer slows evaporation and therefore the cooling. It also keeps wind off the wet fabric. It is not a long term fix, because the moisture is still against your skin, but it can help until you can change. Choose a layer that lets vapour through so the moisture is not trapped completely.

Think about it before you go out

The best solution is to plan for it. Dress slightly cooler from the start so you sweat less along the way. Take off a layer when you warm up and put it back on when you stop. That way you avoid getting soaked in the first place, and your body does not need to spend energy warming up a wet layer.

Frequently asked questions

How quickly do you get cold

In still air within a few minutes, in wind much faster. It also depends on how wet the layer is and how close it sits to the skin.

Is that why cotton is not recommended for sport

Yes, cotton holds on to water and keeps cooling you long after you stop. A layer that moves moisture onwards usually feels better.

Does a layer on top help

Yes, it slows evaporation and therefore the cooling. But the best option is still to change into a dry layer as soon as you can.