Why does Cotton Kill?

Have you ever wondered why people say, Cotton Kills? Do you understand exactly why? Here’s an in-depth explanation as well as a list of other fabrics that you should avoid when shopping for hiking clothes.

Cotton Kills
Is this a Killer?

Insulation

Clothing keeps you warm by trapping warm air near your skin. When cotton gets wet, it ceases to insulate you because all of the air pockets in the fabric fill up with water. When you hike, you perspire,  and any cotton clothing touching your skin will absorb your sweat like a sponge.

If the air is colder than your body temperature, you’ll feel cold because your cotton clothing is saturated and no longer providing any insulation. This can lead to disorientation, hypothermia, and potentially death if you become too chilled. Remember, hypothermia can occur in temperatures well above freezing and become serious if you get wet and chilled.

Wicking and Layering

In addition, wet cotton does not wick water away from your skin. Wicking fabrics move water from wet areas to dry ones using a process called capillary action. For example, a wicking baselayer shirt made out of Patagonia Capilene will move moisture from the surface of your skin to the outer layers of your shirt leaving the part of the fabric touching your skin dry. This is why layering is such an effective clothing strategy for hiking because wicking fabrics move water away from your skin and up through your layers one after another, enabling the fabric near your skin to trap insulating air and retain your body’s warmth.

Wool

Wool does not wick as well as synthetic garments and will absorb up to 36% of its weight in water. Unlike cotton, it does insulate when wet and is considered an acceptable fabric for hiking clothes.

Other Forms of Cotton

Avoid wearing garments that are labeled as corduroy, denim, flannel, or duck. These are all made with cotton. In addition, steer clear of cotton-polyester blends, for example, 50/50. They’ll still kill you, although it may take a little longer.

Other Fabrics to Avoid

Modal, rayon, viscose, tencel and lyocell are all manufactured fabrics made from cellulose fiber. They absorb water even faster than cotton and lose all of their insulation value when wet. You should also be very careful with clothing made from Bamboo, which is often advertised as being a green product having characteristics comparable to wool. Many bamboo fabrics are actually just a type of rayon and share all of its pitfalls.

Silk is also very absorbent and loses its insulation value when wet.

Additional Resources

REI’s How to Choose a Baselayer is a good source of additional information on the comparative strengths and weakness of different fabric types, and provides a good list of synthetic clothing and wool clothing manufacturers.

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19 comments

  1. These people are not newbies or weekend backpackers. You’ve said it. Very experienced people being “very careful”. There are obviously exceptions. But for general advice to keep a hiker warm and safe “Cotton Kills” is a useful rule of thumb.

  2. Hemp falls into the cellulose category….not advised.

  3. How right you are Philip. I learnt this one some years ago when adopting the layering system recommended by the contemporary backpacking manuals. I wore a heavy brushed-cotton shirt (in the mandatory criss-cross pattern) as a mid layer, soon to discover that while the rest of my clothing (apart from the cotton inner socks!) stayed comparatively dry, the shirt was sodden by the end of the day, and I don’t sweat that much. Avoided cotton fabrics in outdoor clothing ever since.

  4. On top of the fact that wool makes me extremely itchy, this is a problem for someone like myself that is allergic to almost all synthetic fibers and have been advised to stick to cotton, silk, lyocell, or tencel… I suppose I’ll just have to layer up and wear synthetic layers not next to the skin!

  5. Great article but please stress that where you wear cotton depends on the climate. Wicking fabrics are not ideal in arid environments like the desert southwest. Too many people come to Arizona to hike when it is 80+ wearing all their wicking materials thinking that they are safe. Cotton stays wet longing, allowing for evaporative cooling to work. This is not the case in humid environments, but fabrics that pull moisture from the skin dry in minutes and can also “kill.” This is coming from someone that has guided hundreds of people in the AZ backcountry for 12 years and has first hand experience with 100s of people traveling from the East Coast and MidWest donning their Under Armor dry fit tees wondering why they are suffering from heat exhaustion.

    • Excellent point. When hiking and running in hot, arid climates getting rid of body heat is essential if you want to avoid heat stroke. Cotton is much superior to wool or synthetics precisely because of its moisture holding properties.

    • Hey Debbie, I’ve always had the opposite advice, I live in inland Australia, blisteringly hot and dry summers (100F and up), I always hike in a synthetic undershirt with a wool or linen top, with wool socks and silk sock liners, and synthetic trousers.

      The advice I got when I was younger was that cotton is like a wet-suit. And I’ve always found cotton shirts feel soupy on me. And that I feel like I’m wearing a wet-suit while moving, then when the sun goes down you freeze because your clothes are damp. I’ve always thought that wicking also keeps you cool because the sweat absorbs the heat then evaporates otherwise it just absorbs the heat then sits on your skin.

      Do you wear a special type of cotton like Egyptian? Or maybe it’s because I live in the mountains so it’ll be high 30’s during the day but then 10c at night so cotton can still kill in those situations.

  6. Paul Randall Dickerson

    About hypothermia above freezing. Several years ago, a boy playing soccer in Tennessee on a windy day began shivering in temperatures around 60 degrees. He was taken to a local hospital, then sent by ambulance to a Level 1 traiuma center. He fully recovered, but only after being put into a device that circulated warm water around his body.

  7. I hike normally in performance dry fit. I work outside in the sun doing very labor intensive work. High performance cotton shirts are a lot more comfortable all day than he dry fit. Cotton is awful in the rain though.

  8. I live and hike in hot areas. Hot dry and hot wet.
    We’re at 80% humidity and range from25 at night to 40 in day.
    Anything other then cotton is going to kill you here. I see a lot of people come from cold climate and have wool blends as they believe they are an all round gear but – no not in the heat.
    Cotton wet creates a cooling system that makes it barable. Obviously you can’t hike in the middle of the day but still if your in anything other then cotton your going to absolutely stink and your going to overheat. – Kakadu NT

    • Actually, synthetic clothes are just as good in hot weather. They’re also much better at protecting you from UV radiation.

    • Hey a fellow Aussie. I have a really different experience. Hiking in the mountains of the SE with temperatures at high 30s to low 40’s bone dry I never hike in cotton. It feels like wearing a hot wet blanket. I usually wear a synthetic base, then a linen or half wool shirt with synthetic trousers and wool socks. But same in the tropics wool or linen shirt. Cotton sticks to my skin and makes me feel like I’m sitting in soup then makes me freezing once the sun goes down.

      I was under the impression that your sweat absorbs body heat then evaporates that’s why wicking keeps you so cool. If it sits next to your skin it’ll just heat up like a wet-suit and make you hotter while active and colder while not.

      I’m also a bit confused by the article; the wool shirt I wear is an icebreaker it’s 40% tencel and it is incredible, I’ve worn it from 40c to -20 and it’s super comfortable and dry, got me through a blisteringly hot and humid Bangkok summer and a Montreal winter. Similarly REI silk sock liners, in a Rust belt summer mid 30’s and high humidity, I’ve never had drier feet. Same with Bamboo, got a pair of socks and underwear recently awesome in hot weather… I feel like maybe the author is mistaken on a few things? Or only referring to cold weather? But while my outer layers change my base is pretty much the same from 40c in the Aussie outback to -20 in the Canadian just with slightly thicker socks and thermals if it’s really cold.

  9. I’m a bit confused by this article.

    So I always wear, Synth base and trousers, wool or linen shirt and wool socks with silk liners. I’m mostly experienced with hot weather hiking (I would never wear cotton in hot dry weather though despite what some other people have said).

    My wool shirt is 40% tencel and my silk socks are 40% nylon. I’ve also tried bamboo socks shirts and underwear, all brilliant in hot weather. I’ve worn my gear from 40C (105F) to -20c (with additions obviously). In fact the silk socks and wool/tencel shirt are by far my favourite. Cool in summer warm in winter. They keep me bone dry while active in high and low humidity in hot and cold weather.

    I’ve had much better experiences with these than with synthetics they keep me much drier, and hence warmer and cooler. I’ve never had drier feet than with my silk and nylon liners. And I’ve never been drier than with my wool and tencel icebreaker.

    I don’t know about insulation but they wick the sweat away so quickly and effectively that they don’t stay damp long in any conditions even when I’ve gotten water in the boots. I’ve heard nothing but good things from adherents of Bamboo, tencel, silk and wool

    So is it the combinations of fabrics that make these so effective? Are you only referring to extreme cold weather? Because I’ve found them effective in extreme cold weather and extreme hot weather.

    I totally agree that cotton kills and as an inland Australian who hikes in high 30’s to low 40’s (100F ish )I disagree with the other commenters who said wear cotton in hot and dry weather. But I’m curious about your no silk, tencel or bamboo stance.

    • What’s confusing? Clothes made with plant fibers take longer to dry. I wouldn’t wear them on cold and hypothermia inducing conditions.

      • And a plastic bag dries even faster. That doesn’t mean people should trade in their synth clothing for trash bags.

        Unlike cotton, linen, silk, tencel and others don’t kill. And you shouldn’t imply they do because you haven’t tried them or don’t like them.

        The confusing part is where you lump all natural fibres together. When some of them are mainstream hiking fabrics with their own pros and cons. And they’re often cheaper and easier to get than good synthetic clothes.

        The difference between many of these fibres and synthetic is so slight that if you are going to get hypothermia in one you’ll almost definitely get it in the other.

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