In a nutshell 💡
- It’s not the fiber that insulates you—it’s the still air it traps: 90 to 99% of the volume of a textile insulator.
- Water conducts heat about twenty-three times better than air. A damp garment doesn’t just lose a little insulation—it changes its very nature.
- Benchmark: a wet cotton flannel shirt lets through about twice as much heat as when it’s dry.
- In wet clothing, you cool down 22% faster at +10 °C and nearly 50% faster at -40 °C. So the problem exists long before the extreme cold sets in.
- Cotton isn’t a bad fabric. It’s a poor choice as a base layer, where it traps your sweat instead of wicking it away.
The cotton T-shirt you’re wearing under your fleece weighs eighty grams. After two hours of hiking uphill, it weighs one hundred twenty grams. Those forty grams are yours, and they’re working against you.
That’s the whole paradox of cotton in cold weather. It’s a comfortable, soft, breathable fabric that people happily wear year-round, including in winter. And it’s precisely because it’s comfortable when dry that people pack it without a second thought—only for it to become the weak link in their entire outfit.
This article isn’t a critique of cotton. It explains exactly how a perfectly adequate material becomes a liability as soon as it gets damp, what the measurements actually show, and what’s being circulated on the subject without any sources. Because on this topic, sensational figures abound and don’t hold up to scrutiny.
What insulates you isn’t the fabric—it’s the air it traps
Let’s start with the point that explains everything else—and one that’s all too rarely mentioned.
A fleece, a down jacket, or a warm sweater doesn’t keep you warm because of the material itself. They keep you warm because their fibers trap a multitude of tiny pockets of air. In a thermal textile insulator, air accounts for 90 to 99% of the volume. The fiber is merely a structure that prevents the air from circulating, and that is the source of all the thermal insulation in a winter garment.
Why air? Because still air is a very poor conductor of heat, which makes it an excellent insulator. As soon as it moves, however, it carries heat away with it: this is why a freezing wind cools you down much faster than still air at the same temperature.
Now, replace that air with water. Water conducts heat about twenty-three times better than air. A wet garment hasn’t just lost a little of its performance: the material that was protecting you has been replaced by one that does exactly the opposite.
This sentence alone is enough to understand the whole problem with cotton in cold weather. In fact, this applies to any material: soaked fleece also insulates poorly, and a high-quality down jacket is no exception. The difference lies in how quickly each material reaches this state—and how quickly it recovers from it.
Just how much does wet cotton actually lose its insulating power?
Here, we’re going to be precise, because this is exactly where the market tends to spout just about anything.
The most reliable data we have comes from a heat transfer study conducted by the U.S. military on cotton flannel. The result, as measured and published: once drying was complete, heat loss dropped by 48%, returning to the level of dry material.
Put another way—and it amounts to the same thing—wet cotton lets through about twice as much heat as the same dry cotton, and retains only slightly more than half of its insulating value.
That’s significant. And it’s very different from the “90% insulation loss” we see everywhere—a figure for which we have found no primary source. We prefer to give you a verifiable measurement that’s half as high as a sensational but unverifiable figure.
A point of clarity is in order: this result applies to this specific flannel, with this particular distribution of moisture and this airflow. As the report itself states, the loss depends heavily on where the water is located within the fabric. It is a measurement, not a universal constant for cotton.
Three widely held claims, and what they’re worth
| What is commonly read | What the sources say |
|---|---|
| “Cotton absorbs up to 27 times its weight in water” | No primary source found. The standardized value is a water vapor regain of 7 to 9% of its mass. The amount of liquid water retained depends entirely on the testing method. |
| “Wet cotton loses 90% of its insulation” | The only available primary measurement gives approximately 48%. |
| “We cool down 25 times faster in wet cotton” | Confusion with the ratio of the thermal conductivity of water to air. The measured body cooling factor is between 1.22 and 1.49 depending on the temperature. |
See also: Does 100% polyester keep you warm? Find out the whole truth!
Wet clothing doesn't just provide less insulation—it actually draws heat away from your body
There is a second, more insidious mechanism, and it’s the one that truly makes the difference between discomfort and danger.
To change from a liquid to a vapor state, water needs energy—a lot of energy. And when that water is in a piece of clothing pressed against your skin, it takes that energy from you.
The orders of magnitude speak for themselves. Evaporating 100 grams of water in an hour removes about 67 watts. Evaporating 200 grams removes about 135. By way of comparison, the basal metabolic rate of an adult at rest is around 80 to 100 watts, and it drops even further as soon as you stop moving.
In other words, a sufficiently damp garment can dissipate more heat than your body produces at rest. Your body then has only two responses: shivering, which costs energy, or letting its temperature drop.
This is no longer just degraded insulation. It’s active cooling, fueled by your own body heat, and it continues until the garment is dry.
How long does it take to cool down in wet clothes?
A study published in 1958 measured the rate of body cooling in wet clothes compared to dry clothes. The results should be read in the correct order.
| Ambient temperature | Cooling compared to dry | What this means |
|---|---|---|
| +10 °C | +22 % | A simple autumn outing or a mid-season worksite is enough |
| -40 °C | +49 % | The effect increases with the cold, but it does not start there |
The same study notes a nearly 55% increase in metabolism when wearing wet clothing: the body compensates, but at the cost of energy expenditure that is 50% higher. Over the course of a long day outdoors, this increased expenditure takes its toll in the form of fatigue.
The most useful figure here is +10 °C. It shows that damp cotton takes a toll long before the bitter cold sets in. Many people gear up thoroughly for winter and completely neglect the transitional seasons, even though that’s when we sweat the most because we haven’t adjusted our layers properly.
More recent research on wet uniforms offers an important insight for those who work outdoors: during short periods of exposure, core body temperature changes little, but peripheral temperatures and manual dexterity deteriorate significantly. The primary consequence of wearing wet clothing is therefore not hypothermia, but a loss of precision in the hands—and thus a compromise to safety and efficiency on the job.
Why does merino wool perform better?
The comparison is instructive because it shows that the question isn’t “to absorb or not to absorb,” but where the water goes and when it becomes liquid.
Merino wool can absorb a significant amount of moisture in the form of vapor—far more than cotton—while still feeling dry. Better yet: by absorbing this vapor, the wool releases heat, a phenomenon known as heat of sorption. The garment warms up slightly the very moment moisture arrives.
However, we must be honest about the limits of this advantage. As soon as liquid water fills the fabric’s pores, wool also loses a large part of its insulating properties, to an extent comparable to cotton. Wool does not eliminate the problem; it merely delays the moment when it arises. This is already significant in real-world use, but it is not a complete solution.
As for polyester and technical synthetic fabrics, their advantage does not come from water repellency, but from their pore structure: they transport moisture outward via capillary action and dry quickly, rather than storing it within the fiber. This is exactly what cotton cannot do, which is why a synthetic base layer remains the ideal choice for any prolonged physical activity.
To learn more: Which fabric breathes best to prevent sweating?
The three-layer system, and the role cotton should never play
The rule that governs all cold-weather clothing consists of three layers, each with a distinct purpose.
The base layer: wick away moisture, never trap it
This is the layer in contact with your skin, and it is the only place where cotton should really be avoided. The INRS puts it bluntly: the layer closest to the body must insulate and wick moisture away from the skin, and damp clothing provides poor insulation against the cold.
Cotton does exactly the opposite: it traps moisture against your body and holds it there. That’s why a simple cotton T-shirt can ruin an otherwise excellent outfit. The heated underwear collection addresses this issue, featuring materials that wick away moisture rather than trapping it.
The midlayer: trapping air
Its role is to create a pocket of still air. This is where fleece, a sweatshirt, or a midlayer comes into play, and where the bulk of your outfit’s thermal performance in extreme cold is determined. A CYCLONE heated fleece with an eco-designed battery fulfills this function while providing additional warmth, which is particularly useful during periods of inactivity. It all comes down to thickness, and this is more a matter of trade-offs than fine-tuning: the thicker a midlayer is, the more air it traps, but the more it restricts movement under technical gear. A thin version can be worn anywhere and provides less insulation; a thick version insulates better but is uncomfortable during sustained activity. Choose based on the balance of exertion and downtime during your outing.
The outer layer: windproof and waterproof
Its job is to protect the two underlying layers from what would damage them: the wind, which sets the air in motion again, and the rain, which fills the air pockets. This is the only layer for which waterproof or highly water-repellent properties are a key selection criterion, and it becomes crucial in extreme temperatures. An eco-designed heated softshell jacket with a battery fulfills this function while remaining breathable—an essential requirement so that the moisture produced by your body can escape. You’ll find all the options in the collection of heated jackets, down jackets, and vests.
A note that applies to all three layers: if the outer layer doesn’t let moisture escape, you’ll get wet from the inside, and you’ll end up with exactly the problem you were trying to avoid. Total waterproofing without breathability is a trap.
Dressing for Extreme Cold: The Key Factors
The temperatures displayed don’t tell the whole story, and this is a common source of error. In extreme conditions, it’s mainly the wind and humidity that determine how cold you feel: dry air at -10 °C is more comfortable than humid, windy air at 0 °C. In fact, there is no legal minimum temperature threshold in the Labor Code, and the INRS points out that risk is assessed based on the combination of humidity, wind, duration of exposure, and the insulation provided by clothing.
Here are some practical guidelines for choosing your gear based on conditions:
- From +10 to +5 °C, while active: This is the range where you sweat the most, because you dress as if it were colder. Opt for a thin, breathable base layer, and be prepared to feel a little cold at first.
- From +5 to -5 °C: the three-layer system really comes into its own, and this is when a hat becomes essential. This is also the threshold at which your extremities become the weakest link.
- Below -5 °C, or in strong winds: Add a layer with high thermal insulation to your torso, always protect your head with a hat and your hands, and plan for an active source of heat during periods of inactivity.
- Extreme conditions or prolonged exposure: Standards for protective clothing exist specifically for extreme cold, and they factor in humidity and wind speed in their assessments. These standards do not specify a specific temperature for use; rather, they define a measured level of performance.
A word about down, often considered the gold standard for warm clothing: its warmth-to-weight ratio remains unbeatable when dry, but it loses its loft once wet—and thus its insulation. Synthetic fillings are more resistant to moisture, though their thermal performance is slightly lower when dry. The right choice therefore depends less on the predicted temperatures than on the likelihood of getting wet, and there is no single material that’s ideal for all conditions.
Protect your extremities, which are the first to feel the cold
The layering principle applies to the torso, but it’s your hands and feet that will let you know first. When your body gets cold at its core, it reduces blood flow to the extremities to preserve what’s essential, and that’s when you start to lose dexterity.
Wearing cotton socks in shoes creates exactly the same problem as wearing a cotton T-shirt under a fleece, with an added complication: your feet sweat in an enclosed space, and the moisture has nowhere to go. The same reasoning applies to a beanie, a scarf, or gloves: wherever a fabric touches the skin and cannot dry, cotton should be avoided, and suitable thermal fabrics are preferable. Specifically for the neck, a heated neck warmer is a better alternative to a cotton scarf, which absorbs moisture from your breath and traps it against your skin. OUTDOOR heated socks address both issues at once—the fabric and the heat output. The complete line can be found in the heated socks section.
“The cold almost never sets in all at once. It creeps in through moisture, several hours after you’ve sweated, when the fabric you’re wearing has stopped doing its job without warning you.”
— Gwenaël Fournet, Product & Innovation Manager at G-Heat
So, should we ban cotton?
No, and that would be a lazy conclusion.
Cotton remains a high-quality material in conditions where it doesn’t get wet—or only slightly: indoors, as an outer layer in dry weather, or during everyday use without sustained exertion. In these situations, it offers a soft comfort that few synthetics can match. Its ability to absorb moisture while remaining comfortable is even an asset in these scenarios.
The key takeaway is more specific—and more useful: cotton is a poor choice as a base layer as soon as you start sweating and can’t change your clothes. It’s a matter of its role in the layering system, not the material’s intrinsic quality.
One last word on a phrase you might come across: “cotton kills.” It comes from the North American hiking community, and its exact origin remains unclear, with no clearly identified author or rescue service. It describes a real phenomenon, but its dramatic tone far exceeds what the data actually shows. We prefer to explain the science behind it.
Don’t miss: How to Spot a Good Fleece: Your Complete Guide
Why Choose G-Heat to Tackle Extreme Cold?
- We address the cause, not just the thickness. When moisture has compromised your insulation, adding another layer doesn’t solve anything. Active heat delivery does.
- A lineup organized by layer, not by marketing category. Base layer, midlayer, jacket: you can add the layer you’re missing without having to buy what you already own.
- Clothing designed for static phases. It’s when you’re at a standstill that your body produces the least heat and accumulated moisture works against you. That’s exactly when heated clothing takes over.
- Products proven in professional settings. The same gear is used by people who work outdoors all winter long. What holds up on a construction site in February will hold up on a weekend outing.
- A standard rooted in the brand’s origins. G-Heat was founded in 2017 by a group of people, one of whom lived with daily sensitivity to cold in their extremities: cold isn’t a niche we added—it’s our starting point. That’s why we make a point of disregarding market figures we can’t verify, like the three you just read.
Conclusion: It’s not the cold that gets to you—it’s the water
Focus on the mechanism rather than the numbers: what insulates you is the still air trapped in your clothing, and the water that replaces it conducts heat twenty-three times better. Everything else follows from this, including the idea that the problem begins as early as mid-season and not just in extreme cold.
So the right approach isn’t to add more layers, but to check what’s against your skin, adjust your layers before you start sweating, and plan for a heat source for when your body stops producing it.
Find the entire lineup in the heated clothing collection, and models designed for your hands in the heated gloves selection.
Whatever the weather. G-Heat, in all weather conditions.
FAQ: Cotton and Extreme Cold
Does cotton keep you warm in winter?
When dry, yes, just like most warm materials that trap air. The problem arises as soon as it gets damp—whether from rain or your own sweat: it traps water against the skin and takes a long time to dry, which significantly reduces its insulating properties.
What materials should you wear in extreme cold?
For the base layer, merino wool or a synthetic material that wicks away moisture. For the midlayer, a fleece or a garment that creates air pockets. For the outer layer, a windproof and waterproof layer that remains breathable. It’s these three layers that make outfits truly warm—much more so than thickness alone: the common thread in this system is managing moisture, not just the cold.
How much does wet cotton lose its insulation?
The primary measurement available, conducted on cotton flannel, shows a heat loss that is approximately twice as high when wet as when dry—meaning just under half of the insulation is retained. The 90% figure frequently cited is not based on any primary source we could find.
Does merino wool really insulate when wet?
It retains its effectiveness much longer than cotton because it absorbs moisture in the form of vapor while remaining comfortable to the touch, and it even releases a little heat in the process. However, once saturated with liquid water, it too loses a large portion of its insulating properties. It delays the problem; it doesn’t eliminate it.
Why do we sweat in extreme cold?
Because physical exertion generates heat regardless of the outside temperature. A sustained climb at -5 °C makes you sweat, and that sweat gets trapped in your layers if they don’t wick it away. This is the classic scenario: you set out wearing too many layers, you sweat, you stop, and you get cold.
How can I tell if my clothes are too damp?
Don’t rely on how you feel while exercising: your body heat completely masks it. Instead, check the layer in contact with your skin during a break, before you start to cool down. On long rides, bringing a spare base layer is the most effective thing you can do.
Is a down jacket sensitive to moisture?
Yes, and for the same reason: down insulates through the volume of air it creates. When wet, it flattens, loses its loft, and therefore its insulating power. Synthetic fillings are more resistant to moisture, though they have a lower warmth-to-weight ratio when wet.
Sources and References
[1] “Working in the Cold: Preventing Risks”, INRS
[2] “Working in the Cold: Regulations”, INRS
[3] “Working in a Cold Thermal Environment”, INRS
[4] “Extreme Cold”, Santé publique France
[5] “NF EN 342: Protective Clothing Against the Cold”, AFNOR
[6] “NF EN ISO 11092: Measurement of the Thermal Resistance of Textiles”, AFNOR
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