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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?

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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11 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.

  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.

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