Why Cotton Kills: Discovering the Dark Side to This Popular Fabric

Cotton is one of the coziest and most practical fabrics there is. It's light, airy, soft against the skin, and cheap to make. It's also, however, all but useless (and potentially deadly) when used in you hiking getup. Learn why this is the case in this article!

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Written by: | Reviewed by: Brian Conghalie
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Certain things just weren’t made to go together. We’re thinking hydrogen and naked flames, orange juice and toothpaste, humans and mullets, socks and sandals. Very worthy additions to that list, for the non-masochistic hiker, are water and cotton. 

Alone, the two are perfectly harmless and, of course, quite useful; combined, their potential consequences for the active outdoorsperson are at best unfavorable, at worst downright deadly – there is a good reason why hikers say “cotton kills”.

So what is it about cotton that makes it such a reliable midwife to mishap, calamity, and catastrophe, and the subject of such ubiquitous scorn among knowledgeable outdoor folks? And what are the best clothes for hiking for those who’d prefer to return home minus a dose of the chills, hypothermia, or in spirit only? 

This article aims to answer both of these questions, dipping into a modicum of science, constructive cotton-bashing, and then providing the skinny on more appropriate outdoor attire.

Key Takeaways

  • Cotton soaks up your sweat instead of “wicking” it
  • Polyester, nylon, and merino are all far better options
  • Cotton can cause hypothermia

Why Cotton Is Rotten

In recent years, the pages of outdoor monthlies and their online newsfeeds have been no strangers to tragic stories of hikers who have died or been hospitalized as a result of wearing inadequate clothing in the mountains and backcountry. In many of these cases, the casualties shared one common denominator: the use of cotton clothing.

Woman hiking in winter cold dark winter forest in warm hiking clothing

Cotton clothing feels soft, is comfortable, and looks better than shiny synthetic duds when we’re going about our regular, day-to-day business, but put to the test of just a short stint of athletic exercise, wet cotton quickly reveals itself to have tendencies bordering on — and occasionally tantamount to — the homicidal.

Water and Cotton

The terms ‘wicking’ and ‘breathability’ are ever-presents in any discussion of outdoor clothing. Wicking is the process by which perspiration filters or seeps (i.e. wicks) through the material of any given fabric from the inside to the outside, thus leaving that material and our skin dry. Breathability refers to any fabric’s ability to allow water vapor to be transmitted through the material instead of trapping it inside.

In terms of breathability and wicking capability, cotton is a very shoddy performer. Instead of transporting the moisture from your body to the outside, it simply collects it, much like a sponge leaving that wet cotton shirt sticking to your back. Cotton garments, in fact, can absorb up to a whopping 27 times their weight in water.

Unlike other fabrics, cotton is so absorbent because its fibers are essentially tiny tubes (called ‘lumens’) that can act as thousands upon thousands of minuscule containers for moisture, thereby leaving us clad in sodden cotton fabric whenever we’re working up a sweat.

Pro-Tip: Be Prepared for Emergencies

In addition to dodging cotton, we’d highly recommend carrying an emergency blanket, even in summer.

If the air temperature happens to be significantly lower than our body temperature, all that water trapped in a cotton garment’s fibers will soon leave us feeling chilled because the garment is not only failing to provide any insulation but also actively decreasing our core temperature at the same time.

Why Being Wet is a Problem

Water can conduct heat away from the body up to 25 times faster than air. As such, staying skin dry in the outdoors is all but a prerequisite to staying warm.

group of hikers with trekking poles walking up mountain scree slopehiking clothing intext

Garments like cotton shirts and cotton jeans flaunt this requirement on two grounds. First, by their absorption of moisture. Secondly, a subsequent loss of insulating properties. When dry, cotton garments provide insulation by trapping air between themselves and the skin; when cotton gets wet, this buffer between the cotton and the skin disappears and increases our exposure to radiant heat loss. 

Being wet in and of itself is not exactly one of the hiking world’s cardinal sins — there are a few of us, for example, who will gladly douse our shirts in water while out on a hike in crazily high temps, or who have left our waterproof rain pants at home, and taken a good soaking in a rain shower, yet lived to tell the tale. Many desert hikers wear cotton and extol the virtues for its capacity to keep them cool when the mercury’s through the proverbial ceiling.

The problem starts when that wetness is allowed to cool down excessively owing to any of a number of factors: injury, rest stops, altitude gain, nightfall, getting lost, a change in weather conditions, descending instead of ascending, moving at a slower pace.

For hikers, the process frequently goes something like this: we start off on our hike, gradually building up a sweat as our graft gets underway; that sweat begins to douse our cotton shirt but remains warm due to our continuing exertions and body heat; then the trail turns downhill, the sun drops, the wind gets up, or we pause to take a photo/pee/look at our map etc.; suddenly that warmth is a distant memory, we are chilled to the bone, and our core temperature is headed dangerously south.

mature backpacker on a mountain ridge in hiking tights

The above is a fairly textbook example of the onset of one of the outdoor world’s most common and life-threatening ailments: hypothermia. 


Over 1,500 people die from hypothermia each year in the US alone.

Hypothermia occurs when our bodies lose heat faster than they can produce it, and when our core body temperature drops below 95F. The early symptoms of hypothermia include disorientation, shivering, a weak pulse, confusion, drowsiness, memory loss, and lethargy. The latter is a loss of consciousness and, if our core temperature drops too low, heart failure.

Being exposed to variations in weather conditions and fluctuating temperatures, straying far from shelter, and perspiring heavily all combine to make hikers a demographic that is at particular risk of contracting hypothermia.

While maintaining a healthy core temperature might seem like an easy task in the year’s more clement seasons, this is in fact exactly when the vast majority of hypothermia cases are recorded. Relatively few occur in the winter, principally because at this time of year we tend to take extra care to ensure we’re suitably dressed and equipped.

Man hiker looking over fjord panorama intext

In summer, spring, and fall, we’re far more likely to be more casual in terms of clothing choices and underestimate weather conditions. In fact, the most important take-home of this article — beyong cotton’s insuitability for hiking — should be that hypothermia can strike at almost any time, even in temperatures well above zero.


April 29, 2018, saw the most deadly day in the European Alps since World War One’s infamous White Friday, with 14 mountaineers and ski-tourers perishing in 5 separate incidents. Though debate still rages on regarding where to place blame for the incidents, the general consensus is that an underestimation of weather conditions and ill-preparedness were keys factor in at least 7 of the deaths.

Following a week of high temperatures, a freak blizzard caught each of the parties unawares, underequipped, and unsuitably attired. Without wishing to do a disservice to the deceased, it is a story we have heard all too often before, and one that echoes — in nature if not degree — countless other hiking tragedies across the globe.

Being caught unawares is an eventuality all of us can avoid. The first step we should take in order to ensure our well-being in the outdoors is adequate preparation, and the first box to tick in this respect is ensuring we wear appropriate clothing, and wear cotton only in town. A condensed working definition of ‘appropriate’ reads something like the following: “high-wicking, breathable, insulating, and devoid of any trace of cotton.”

hikers on winter hike in deep snow intext

Thermal Value

Years ago, following the deaths of several hikers in the early 1960s, a series of experiments conducted by the Royal College of Surgeons (which included Dr. Lewis Griffith Cresswell Evans Pugh, the physiologist who had been crucial to the successful summit of Everest in 1953) discovered that the “thermal stress” responsible for each of the deaths was a result of inadequate clothing.

Although the victims had been wearing an ample amount of clothing, their demise was expedited by its form: jeans (denim is a form of cotton), cotton t-shirts, cotton underwear, and sweaters made of wool-cotton blends. The subsequent experiments found cotton garments to have a thermal value of next to zero when exposed to wet and windy conditions.

How Other Fabrics Keep You Warm

So, what do other fabrics do that cotton does not? The short answer goes something along the lines of the following: “wick”. A more detailed answer for different fabrics is given below.


Let’s start with the drawbacks. Wool hiking underwear and mid-layers are, generally speaking, a pricier option that can take a long time to dry out when wet. It also doesn’t wick moisture quite as well as high-performing synthetic fabrics and can absorb up to 35% of its own weight in water.

The positives are that wool is a massive improvement over cotton. Not only does it continue to insulate when wet, but it also offers a better warmth-to-weight ratio than most synthetic products, is highly breathable, and wicks reasonably well. Some merino wool synthetic blends, such as those produced by Icebreaker, offer much better performance wicking-wise.

Thru Hiker making his way along trail intext

The fibers in any wool garment’s outer layer comprise a microscopic coating called an ‘epicuticle’. This layer acts as both a repellent to water and wicks vaporized water molecules (i.e. sweat) away from the body, into the clothing material, and then out again as a result of spreading the liquid over a larger surface area, thus facilitating evaporation. Additionally, wool fibers provide insulation even when wet thanks to millions of tiny air pockets that form in the gaps between each fiber.


Synthetic products made specifically for athletic exercise and the outdoors come in an array of forms and with varying specs. Their efficiency, however, is measured by one key feature that distinguishes them from everyday, non-technical garments. You guessed it…wicking capacity.

Each of the big brands such as Gore-Tex or Primaloft outperform cotton products by a) transporting moisture from your body to the exterior of the fabric, where the process is then repeated by a subsequent layer (or, if you’re only wearing one layer, evaporating in the ambient air), b) providing some degree of insulation even when wet, c) drying quickly, d) retaining breathability.

Pro Tip: Not All Synthetics Are Great

Not all synthetic materials are the gold standard of wicking capabilities. In fact, some even outperform cotton in the ‘useless when wet’ and water-retention stakes.

Some of the more common fabrics to avoid include rayon, viscose, modal fiber, Tencel, and Lyocell, all of which are synthetic but comprise some degree of the same cellulose fiber responsible for cotton’s sponge-like absorption.

Although silk garments were de rigueur at the time of the early European expeditions to the Himalaya, their use was only effective at high altitudes, where the climate is far drier than where most of us do our hiking. Though not as poor a performer as cotton, silk is another weakling wicking-wise and offers all but zero insulation when wet.

Layering System for Clothes

As covered in our more detailed analysis on How to Layer Clothes for Cold Weather, layering is essentially a means of effectively managing body temperature regulation through the use of breathable strata of garments that wick perspiration away from your skin whilst retaining body heat between each layer. 

backpacker wearing 3 layered clothing system intext

The standard layering setup consists of a baselayer, mid-layer, and outer layer. Each layer has its own function, with the baselayer fundamental to moisture management, the mid-layer all about insulation, and the outer layer providing protection from the elements.

Pro Tip: Be Proactive

Don’t wait until you’re peeling ice from your skin before adding a layer — once your core temperature drops, getting it back up again can be a tricky business.

Cold hands and cold feet are usually not so much symptomatic of substandard socks, boots, or gloves, but of a dangerously low core temperature — if you start to feel the nip, don’t ponder a remedial gear purchase but throw on another layer instead.

In each layer, breathability and wicking are essential: should any single layer not do both adequately, the whole system breaks down. As such, any layering system that contains cotton is destined to fail.

Cotton Kills: Wrapping Up

We hope you have enjoyed our article, and have a better understanding of (1) why cotton sucks, (2) why you shouldn’t wear cotton when hiking and (3) always be prepared, as hypothermia can strike even in “fair weather”.

If you have any comments or questions then please comment below.

Last update on 2023-10-01 / Affiliate links / Images from Amazon Product Advertising API

Kieran Avatar

Kieran James Cunningham is a climber, mountaineer, and author who divides his time between the Italian Alps, the US, and his native Scotland.

He has climbed a handful of 6000ers in the Himalayas, 4000ers in the Alps, 14ers in the US, and loves nothing more than a good long-distance wander in the wilderness. He climbs when he should be writing, writes when he should be sleeping, has fun always.

Kieran has taught mountaineering, ice climbing, and single-pitch and multi-pitch rock climbing in a variety of contexts over the years and has led trekking and mountaineering expeditions in the Alps, Rockies, and UK. He is currently working towards qualifying as a Mountaineering and Climbing Instructor and International Mountain Leader.

Kieran’s book Climbing the Walls—an exploration of the mental health benefits of climbing, mountaineering, and the great outdoors—is scheduled for release by Simon & Schuster in April 2021.

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