Why Cotton Kills
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.
It 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, 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 moisture 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. 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’) which can act as thousands upon thousands of minuscule containers for moisture, thereby leaving us clad in sodden 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 dry in the outdoors is all but a prerequisite to staying warm.
Cotton garments flaunt this requirement on two grounds. First, by their absorption of moisture. Secondly, their subsequent loss of insulating properties. When dry, cotton garments provide insulation by trapping air between themselves and the skin; when wet, this buffer 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 even extol the virtues of cotton 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 apparel 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.
The above is 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 are 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.
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 — beyond the inadequacies of cotton — 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 a 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 wellbeing in the outdoors is adequate preparation, and the first box to tick in this respect is ensuring we wear appropriate clothing. A condensed working definition of ‘appropriate’ reads something like the following: “high-wicking, breathable, insulating, and devoid of any trace of cotton.”
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 a wool-cotton blend. 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 is, generally speaking, a pricier option that can take a long time to dry out when wet. It also doesn’t wick 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 on cotton. Not only does it continue to insulate when wet, it also offers a better warmth-to-weight ratio than most synthetic products, is highly breathable, and wicks reasonably well. Some wool-synthetic blends, such as those produced by Icebreaker, offer much better performance wicking-wise.
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 liquid (i.e. sweat) away from the body, into the 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 (technically, ‘crimps’) 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.
Some of the more notable, big-brand forms of high-wicking, breathable fabrics include Capilene, Dry-Line, Cool-Lite, Primaloft, Coolmax, Polarfleece, FlashDry, and Gore-Tex (outer layers and shoes/boots). If in doubt, the bottom line is that polyester-based products do not absorb moisture.
Each of the above 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 altitude, 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 through the use of breathable strata of garments that wick perspiration away from your skin whilst retaining body heat between each layer.
The standard layering setup consists of a baselayer, midlayer, and outer layer. Each layer has its own function, with the baselayer fundamental to moisture management, the midlayer 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.