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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?


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 capilary 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 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 labelled 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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  1. Hi, Earlylite.

    I guess you know what's coming. From a Brit, of course.

    "Ventile is a high-quality woven cotton fabric first developed by scientists at the Shirley Institute in Manchester U.K. during the Second World War, for use in pilots' immersion suits. Ventile has a reputation of being both waterproof and windproof. It is hardly found in the United States, but in Europe, especially in the UK, it has seen a revival with the bushcraft movement. It is popular with birdwatchers and naturalists because, unlike synthetic fabrics such as Gore-Tex, it produces almost no noise when in use. It is very popular among survivalists and bushcrafters in the European forests because of its strong resistance to tearing and fire."

    One helicopter I rode in had a notice up instructing that synthetics should not be worn as they fuse with the skin in the event of fire. (My dad's fireman's coat was heavy duty wool). I only tried ventile once and, in a single layer, it was less successful than claimed. I got cold and wet, but the double layer stuff is supposed to be good.

    As far as ordinary cotton is concerned, the only real misconception is that it is slow drying. If made into a thin fabric, cotton dries rapidly and as it gets smelly much less quickly than synthetics, cotton is what my backpacking boxers are made from.

    • I think the main reason Ventile is so popular in the UK is because Ray Mears sells it on his website. Him not being on TV here in the US, I think, is a big factor in why so few people attempt to wear it here.

      In my experience, it is a horrible material. It does not do any of the things it is advertised to do. It is not waterproof (even the double Ventile), and when wet, it is as breathable as a plastic bag. When dry it does make a good wing shirt, but mind you, the world’s heaviest wind shirt. If at some point you have to take off your double Ventile jacket, presumably when walking, you need a separate backpack just to stuff it somewhere.

      There are so many synthetic materials on the market, with such a huge range of properties, that if one has to resort to cotton clothing, he is not looking hard enough. I think this is one of those instances where fashion has overridden utility. I know we all want to be like Scott and Mallory, but it was not the clothing that made the men.

  2. As Zed has pointed out cotton outer garments, especially Ventile, can work well.

    50/50 polycotton is actually good stuff. I wore it all the time before synthetics like Supplex and Pertex appeared. I hiked the PCT and CDT in polycotton trousers, shorts and windshirt and I'm still alive! Modal, viscose and bamboo can be good too, depending on the mix of materials. I've used all three and found them fairly fast wicking and drying and quite comfortable.

  3. Why is this "myth" still perpetuated? Like merino, capilene, polyester, nylon, etc. cotton does have a place in the spectrum of outdoor garment materials. Generalizing across the board that cotton "kills" is rather foolish I think, that's like saying across the board that down "kills" because it's not an ideal insulation material in sustained cold/damp environments. I think there are many instances where cotton is just fine, especially used on summer trail walks.

    I live in the high desert southwest of New Mexico where the humidity is next to nothing most of the year, our air is extremely dry and the sun relentless and high, thin cotton is one the best materials for staying cool and dry. I've found synthetics like Capilene 1 to retain too much heat, the surface of the material warms up and the material doesn't breathe as well as a thin cotton or 50/50 blend. Just my experience. I have no qualms about heading out for a few days into the backcountry in June with a thin cotton shirt.

  4. Cotton is GREAT, during hot summer days…….. It's not all doom and gloom.

    • AGAIN, the author WAS NOT talking about hot days or staying cool. He was talking about staying dry when it’s cold and you’re perspiring a lot. Which is precisely where cotton fails, exactly as he said. Reading truly is fundamental.

      • Again, the first two sentences say avoid cotton in hiking clothing. It never mentions when it is appropriate, thus leading novices to believe it never is appropriate. Your condescending tone is unnecessary.

  5. Very good article. This is true of cotton that I have discovered myself while hiking. Even on a hot and sunny day hike, even if I am just wearing a single cotton tshirt, my back will get sweaty from my backpack, and will not dry, even in the wind. This can get uncomfortable really fast. It is always best to choose a synthetic base layer.

    One question I do have. Some people have recommended to me to wear a tight fitting base layer such as under armor as these tight against the skin base layers wick better than a more loose fitting base layer like something like a more loose fitting tshirt made of similar material. In your experience, does this make a difference at all or would this just be a personal preference of fit?

  6. I used to wear cotton on day hikes and my back would get soaked and I would freeze at the summits. I would take my shirt off and dry it on a warm rock in the sun when I could. Once I started wearing poly I realized my mistake and I've had much drier and warmer hikes since then. Also snowboarding I threw away all my cotton long underwear and its made a HUGE difference in sweat management as well as pit zips. I still see a lot of people drenched in sweaty shirts at summits, struggling to dry out. The only cotton I wear on a trip stays in my car for me to change into when I get off the trail. All my non-summer hiking & boarding clothes are also black for that extra warmth on cold sunny days.

  7. Hi, again.

    I agree with all of the above. Cotton in a desert? Definitely.

    Cotton t-shirt for ascending to a big, cold summit? No way.

    Cotton t-shirt getting cold and sweaty fast? Absolutely.

    Thick cotton garments absorbing so much water that they dry out slowly? Yes.

    Photographs of cotton fibres show them as hollow tubes, which insulate well, when dry but which collapse when wet, becoming significantly less effective as insulation. I use cotton only for boxers when backpacking and admit that the waist band can get damp but the odour advantage over synthetic grundies is so great that I put up with the dampness. I have also found that M&S thin cotton boxers are ready to wear after a wash at least as fast as Rohan synthetic boxers so I'm happy with M&S for extended backpacking trips. The Rohans live in my big kayak bag for wearing in the car after a capsize. In other words, I don't like them at all.

    A Ventile jacket for birdwatching would be great. Sadly, the price is astronomic. The vendors claim a Ventile jacket will last a lifetime…

  8. @Shawn – I often wear a tight synthetic layer during 3-season climbs. They wick fast, and I find them comfortable. Skinz are a really well-made brand, but pricey. Cheaper alternatives are Sugoi and UnderArmour.

  9. Living in Texas, I wear cotton every day. I also wear it when flying, on the very off chance I might need to evacuate an aircraft on fire. I also wear it for day hikes in the desert. However, when overnight hiking, I wear synthetics because of the weight advantage and safety issue if it gets wet. Most of my backpacking is in the cooler months and getting and staying soaked would be a real bummer.

  10. It sounds like climate, whether hot or cold, dry or humide and possibly other variables such as altitude have a lot to do with how you dress and what fabrics to wear.

  11. Cotton in hot weather is just fine because it will hold water and help keep you cool. It really only becomes problematic when the temperature starts to dip, you stop moving and cool, or you experience significant wind chill. The problem comes when the temperature starts to and/drop below the point where your body heat can keep you warm. I simplify my closet by hiking in synthetics all the time and also because wool creeps me out. I think I'm allergic to it or something.

    You can obviously overcome the compromises of a 50/50 cotton/polyester blend by wearing other insulating/wickling layers/shell layers on top of it and by walking fast to keep you body heat up. If you think of a hard shell as a vapor barrier, you can pretty much wear anything under it and stay warm, as long as you don't take it off. Chafing and blistering are another issue, of course.

    I just wanted to explain the logic behind the claim about Cotton Kills – because it seems like few writers ever do, and assume you know, and also to call out the problems with the cellulose fabrics which are hidden in a lot of advertising bs.

    This Ventile stuff sounds interesting.

    • What are your thoughts on this? I know these are just movies, but Indiana Jones always wore cotton pants and shirts with a leather jacket in both humid and desert climates. Are those clothing combinations really practical and if so, why? I have tried them myself, and even though it causes me to sweat, obviously, I am relatively warm yet cool as well. Thoughts?

  12. You bring up something I almost forgot about when it comes to cotton. The chafing. This is a major problem for me in the cold winter months. Cotton boxers and cotton jeans make me chafe and itch after walking only a couple of miles. Unacceptable. This is where synthetics are great.

  13. > As far as ordinary cotton is concerned, the only real misconception is that it is slow drying.

    My experience is with thin cotton is that it is still very slow-drying.

    Note that not all synthetics are created equal. For example, acrylic is slow-drying.

    I think the only good choices for conditions which may be life-threatening are polyester, nylon, and possibly polypropylene.

  14. As Phil says, it depends on where and when to use cotton. Cotton breifs are about all I use though, though that's because I do not bother with swapping gear around for the seasons.

    The past weekend showed the problem with poly base layers, too. Unlike good UL merino wool, they are much thicker, around .3mm for merino wool and about .8mm for poly. A tight base layer is important for wicking and becomes less important for insulation. Skin tight is good for distributing perspiration over your entire skin surface, not just at the pores. Cooling becomes more efficient, overall. Better than cotton which stretches and gets quite baggy. My partner was struggling to keep cool even at 37F wearing his light-weight poly base. (Climbing the High Peaks area is often work.

    A second layer of mid-weight merino wool adds a lot of insulation value, even damp or wet. Again, this should be firm fitting but not skin tight. With a layer of fleece over this, we paddled many miles in ADK "mist" (a cross between rain and fog.) When we got to the shelter, we were soaked, but not cold at ~44F.

    For sleeping, a layer of light, mid or heavy merino wool is basic. It absorbs some sweat and more importantly, it has an afinity to body oils, unlike cotton. The lanolin can adsorb a LOT without transfering to the sleeping bag. It also doubles as the "Oh Sh!t" layer.

    The only time I found poly and capaline materials really good was in winter. They seem to outperform the merino wool because they are thicker. They did not seem to be any better at distributing sweat when climbing, though.

  15. I stopped buying cotton clothes when I got serious about hiking and I have to say I have found nylon garments to be fantastic. The technology today which can make nylon into soft, safe hiking clothing is amazing!

    Nylon and wool clothing, yes. Cotton, never again! Why would I spend money on a piece of clothing I had to be super aware about? Things happen. Be prepared and since wearing cotton can be a liability, I choose to wear other fabrics.

    But, I do love my Egyptian Cotton 300-thread count sheets, but they will never accompany me into the Olympics, so this is my one cotton indulgence. :)


  16. Like so many things, it’s just not that simple. Cotton absorbs water very well, that’s why terry cloth makes good towels. Synthetic fibers are solid fuel. I don’t wear synthetics when I expect o be around fire. This is where the cotton-poly fabrics have their niche. They don’t absorb as much water as cotton, but they don’t catch fire. As far as I am concerned, an acrylic flannel shirt is one of the warmest shirts and acrylic socks are very warm, but they burn. I do wear fully synthetic base layers in cold weather, but my outer layers tend to be wool or blends. Cotton doesn’t kill, choosing the wrong clothing for your circumstances does.

  17. Looking for some good strong hiking clothing that isn’t a synthetic. I was wondering if hemp clothing is good? I know it’s very strong and that’s about all I know. Any help would be appreciated!

  18. Cotton does not kill.

    I have worn cotton for many years in the mountains with no ill effect.

    Depending on weather conditions, time of year, and activities undertaken., determines whether or not I wear cotton, wool, or a wool /synthetic blend.

    One should choose the proper fabric for the environment one is in.

    Once again, a foolish myth rears it’s synthetic, oil based head.

  19. Cotton said, “Haters gonna hate!” Cotton rules!

  20. In 1992, Sir Ranulph Fiennes and Michael Stroud crossed Antarctica unsupported wearing only cotton technical clothing. As I recall from Mind Over Matter, they were very careful about how much they wore on any given day so as to not overheat and sweat too much, but I think they also felt that nothing would breathe as well as cotton.

    • 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.

  21. “I have 4 or 5 pair of ‘hunter green’ filson pants made of 100% wool, and it is a heavy grade of material.

    Those are the only pants I wear all winter long. -20F is no big deal in those pants. So far I have not needed long underwear.

    In the early spring, tapping maples, carrying sap in a backpack, on snowshoes, I have punched through the ice into flowing river water, a few times. So far, each time, I have been able to catch myself on the ice at my armpits. Toss off my backpack, and crawl back up onto the ice. Thoroughly wetted-down, and so far I have not lost a pair of snowshoes in the process.

    Once I get to walking again, half-way back to the house, I am warm again.

    I may be seriously wet, but, wool means that your warm.”

  22. Wow, this is so weird to me… I seem to be an alien… for me it’s the synthetics that make me chafe, and make me overheat and sweat so much that I’m saturated beyond any fabric’s wicking capability. The only synthetic I will ever use for inner wear is rayon/viscose, and then only when I have to. I also find that my skin gets yeast and bacteria overgrowths with synthetics.

    I hike for fun and fitness, I’m not one of these crazies that aren’t happy unless they’ve hiked the Rocky’s and the Himalayas. When hiking in the cold I find that I must limit my pace to avoid saturation… I have never considered hiking to be a ‘race’. I also avoid places with extreme sudden changes in conditions, where you could be racing for your life. That can happen anywhere, but no use being all macho idiot, and taking extra risks. I use lots of light woollen and linen blends for the cold, (speaking of innerwear), similar to the traditional fabrics found in mountainous areas. Humans have survived for centuries in extreme conditions without synthetics. Most of those survivors were sensible enough not to push themselves beyond sensible limits “because my real life is that boring, and I need what someone else told me was a challenge.”

    I also use furs and leathers for outer wear, when appropriate. They keep the wet out beautifully. Light woollen hose and leather trousers is the warmest and driest combo I know. The leather requires some upkeep, so as not to stiffen in the wet, but nothing hard to do. I don’t think I’ll ever be able to catch and skin/eat a polyester bear in a ‘hiking trip gone wrong’ type scenario.

    Having said all that, synthetics have their place, especially for those with no reactions to them. Not using an available tool is silly. Yes synthetics wick faster, but I find that they up the need for wicking too quickly, and too heavily. I can go a lot further without overheating in natural fabrics.

  23. When you’ve started off exercising in cool weather and built up some heat, even with delayering, cotton next to your skin can really chill the body if you have started to perspire. That is a terrible feeling. I have seen novice cross country skiers over dressed in heavy parkas, hats and gloves who struggle and sweat and the next thing they know, as they pause to regroup, they are shivering because of improper layering and most likely the use if some type of cellulose or cotton product. Synthetics have made significant improvements over the years as some polypro now includes an antibacterial component to reduce the body odor. Also there are brands, such as SportHill and Swix, that specialize in long briefs for both men and women and pants that are wind proof on the front, but diaphanous on the back to allow perspiration to escape. The technology is there, comfort is better and prices have come down so that people should be able to find an appropriate synthetic. I personally love cotton in the summer, but know that on a sweat-inducing hike, a synthetic is better for when both the temperature and I cool down.

  24. Quick question: I’ve got a polyester base layer and a mario wool sweater, but then a 50/50 blend for a sweatshirt underneath my insulating jacket… underneath my shell. Would it be best to find a fleece to replace the half cotton, half polyester blend, or do you think this would be okay for long distance backpacking in the winter followed by a Pyranees hike during Spring?

  25. Somebody explain me this: lakes freeze only after the air is below freezing for a long time, right? And who hasn’t been swimming in the cold and have stayed comfortable while in the water, but frozen when getting out into the air? Water retains heat better than air.

    • Frank: Water has a much higher specific heat than air. If you were in a pool of warm water, it would feel much warmer than being in air at the same temperature. The catch is, water is an excellent conductor of heat, much better than air. This is why you want to trap air next to your skin, not water. If the outside temperature is lower than your skin temperature, water will suck the heat right out of you if left in contact with your skin. If you doubt it, try getting out of the shower wet on a cold morning in a chilly bathroom. Drying yourself makes you feel much warmer almost immediately, even though the air temperature in the room hasn’t changed much at all. Cheers. PS, I like hiking in the Anza Borrego in cotton, as long as the air temperature is above 90F. Remember you can get hypothermia on a moderate summer day.

    • Different concepts Frank. When you get out of the water you get colder regardles of how cold the water was. If you air dry yourself you are using your own body heat to evaporate the water droplets. You lose heat therefore you get colder. The latent heat of evaporation for water is quite high therefore you surrender quite a lot of heat. You may notice you get cold even when getting out of a shower on a hot day. Suck your finger and hold it up to determine the wind direction, the cold side is the direction of the wind because the moisture is evaporating faster on that side, it is losing heat faster.

    • Hi Frank. The case you desire is because the water is warmer than the surrounding air. Any scuba cover will tell you water extracts heat very fast. In fact 24x faster than air. This causes the ever present risk of hypothermia, even when in seemingly warm waters. Additionally water evaporating from wet skin has a cooling effect, this is how your fridge works by liquifying the refrigerant under pressure and allowing it to return to gas at room temperature you and achieves temperate significantly folder than the ambient temperature.

      Cotton may not kill but physics often does!

  26. I hate the feel and especially the smell of synthetics. I’ve recently switched to light merino tops but I also occasionnally use 50/50 cotton/polyester t-shirts and I don’t find that they take much more time to dry than pure synthetics as long as it’s a thin layer. For pants and shorts I stick to synthetics as I don’t sweat as much and thus the odor remains acceptable.

  27. Yes synthetics tend to stink quite quickly.Ok if you can wash each day, and they do dry quickly. My wife and I bought bamboo underwear and socks thinking they were environmentally friendly. They take forever to dry, whereas our Icebreaker merino woolen underwear dries overnight, just sqeeze the water out by hand a few times as the water sinks to the lowest point whilst on the line.

  28. Realised after I pressed send that I’d gorgotten to mention that Icebreaker underpants don’t seem to last as long these days. The seem to get holes faster and the material splits easier. They appear to be thinner. They certainly dry fast as there is bugger all material there to hold water. Maybe this has happened since the have been made in China.

  29. The author of the article just told us that many thousands years of human body evolution must be neglected because the want to sell more smelly plastic.
    Yes! You should not use cotton as a base layer during cold wether. It is right only for cold wether around 7 degrees C and high altitude above 4000 meters. Just use wool instead of cotton.
    During hot wether more than 12 C it is better to use cotton to cool your body. Plastic force your body to produce more and more sweat. Sweat is not just water! It is also minerals and solt!! Plastic base layer destroy the balance of your body extracting more sweat then needed to cool your body. With plastic first layer your body looses much more energy then necessary.
    Sorry for my English but the author of the article does not tell all necessary information.

  30. If you’re old enough, you know this. “Cotton kills” is a marketing slogan from the seventies, coined by the polypro industry. Countless articles and lectures over the years propagated it as some kind of wisdom. That makes it one of the great brainwashing accomplishments of all times. Just look for old copies of “Wilderness Camping” and you can probably pinpoint the year it started. The proof given usually involved someone dying from poor judgement and synthetics wouldn’t have saved them anyway. I marvel at how long this has gone on.

    It’s bad judgement that kills. What you’re wearing may make it worse. But people survive in cotton everyday. Every day.

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