Cotton is Cold

There is a saying in the outdoor world that goes, “cotton kills”. It’s a dramatic way of expressing that cotton is not a suitable clothing material to take with you into the great outdoors. The reason being that it wicks body heat away from you when it is wet.

My favorite example of is a story from a week long mentorship program I took in the Pacific Northwest several years ago:

After our first night sleeping outdoors midsummer in the Pacific Northwest one of the women in our group reported she had been cold in her bed overnight and asked if she could borrow a blanket from someone.

The next morning, same thing.

She had been cold in the night and did someone else perhaps have a blanket she could add. Note that it was summer time and she had a sleeping bag and two an extra blankets.

Third morning, same thing, she was still cold.

Now I am not really one to add my two cents when there are plenty of knowledgeable adults around perfectly capable of helping this woman.

However this had gone on long enough, it was my turn to meddle.

I went over to her and began asking her more questions about her sleeping arrangements so I could paint myself a clear picture of her setup.

Finally I asked, “what are you sleeping in?”

To which she replied, “my pajamas.”


I suggested she sleep naked and see what happens.

The next morning she came to breakfast carrying both extra blankets and thanked me for her first warm nights sleep since she arrived.

The culprit? Cotton pajamas.

You see most of us sweat while we sleep.

This made her pajamas wet and the wet fabric was wicking heat away from her body. So while she may not have actually been cold she felt cold. Which when you are sleeping may as well be the same thing.

Here is the scientific explanation why:

When we say ‘cotton kills’ we are referring to an increased risk of hypothermia.
Hypothermia can occur at any temperature and children with their small bodies are particularly vulnerable.

Cotton is really good at absorbing water.

Think of your best bath towels vs those cheap microfiber ones.

Wet clothes will constantly wick the heat away from a child’s body as the water tries to be the same temperature as the body it is in contact with but is being cooled by the air outside.

Cotton stops being warm when it gets wet because the insulating air pockets fill with water and water is very good at conducting heat.

Water is really good at conducting heat.

Water will become the same temperature of whatever is around it very quickly. It begins this process almost instantaneously.

Which means a wet piece of clothing will pull heat from your body 25x faster than a dry one.

At temperatures below freezing anything that is wet will quickly begin turning to ice.

And that is why we say ‘cotton kills’.

Stay dry = stay outside!

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