Illustrations: Sophi Gullbrants

Two Septembers ago, a South Dakota snowstorm caught me off guard. I packed light — too light — for a trip to the Black Hills, to participate in the Buffalo Roundup and Arts Festival at Custer State Park. Huddled in the bed of a pickup truck in the middle of a thundering herd of buffalo, wearing every article of clothing I had and still cold all the way down in my bones, I swore I’d never be unprepared for the conditions again.

This winter, as the ongoing pandemic makes it unsafe to gather indoors, you may find yourself spending more time outside if you want to do any socializing, braving low temperatures and less-than-ideal weather in many parts of the country. You may not have plans to race across the frigid prairie chasing buffalo, but even if you’re just having some backyard beers with your friends, the same concepts apply: Preparation is key, clothing choice is all-important, and understanding the science of warmth can help you hang onto it.

Your body is constantly producing — and losing — heat

“For us to have our metabolism, our cells being alive, [that] takes energy,” says Christopher Minson, PhD, a thermal physiologist at the University of Oregon. “The byproduct of metabolism is heat, and that’s why we have a body temperature.”

But as your body constantly generates heat, it also needs to get rid of it to not overheat, and there are three primary ways that happens: conduction, convection, and evaporation.

Conduction happens through contact with surfaces. If your body temperature is higher than the things around you, you’ll lose heat when you touch those things. “Different materials have different conductivity,” Minson says. “Metal, for instance, really conducts a lot. You’ll lose a lot of heat to a metal surface, vs. plastic or something else. Even wood is much better at not conducting heat.”

Here’s the first piece of advice: If you’re planning an outdoor event, consider the furniture. If you skip metal folding chairs in favor of seats made of wood, fabric, or plastic, conduction will decrease and you and your guests will automatically stay warmer.

As for convection, “If you’re standing in a current — whether it’s water or wind, that’s convection,” says Minson. As air moves around you, it pulls heat away from your body. The calmer the current, the warmer you’ll stay, but this one is a bit more complicated in the context of safe socializing, because when it comes to reducing Covid-19 transmission, airflow is your friend.

So, rather than erecting a tent (which isn’t guaranteed to lower risk of infection), find other ways to keep the wind from whipping away your warmth. You can try an umbrella — it can act almost like your own personal enclosure — to reduce heat loss through convection, or other accessories, like a tight-knit balaclava or wind shell jacket, that cut the wind.

And don’t forget your feet: “Running shoes are well-ventilated so your foot doesn’t overheat,” Minson says, which is great while you’re exercising, but less helpful when you’re just hanging out. “Wear something that covers your shoes to keep air from getting in, or choose shoes that keep wind out. Leather is a good choice.”

When thinking about what to wear, keep in mind the third, and possibly most important, method of heat loss: evaporation.

What really determines how comfortable you’ll be isn’t the layers you wear, but what they’re made of, and what’s between them.

Your body is constantly producing moisture, and the evaporation of that moisture is the foundation of the human thermoregulation system. Sweat evaporating off your skin cools you down in summer. In winter, the cooling effect is a lot less desirable, but you still need to get rid of the dampness. While a totally impermeable outer layer might keep the wind out, it could also lock your moisture in, and that’s not necessarily a good thing.

“The idea is you need a balance, especially if you’re moving around and generating some heat,” Minson says. “You need some ability to lose the water vapor from your skin. If you wear a plastic bag, there’s no ability for humidity to escape from your body.” If you’re moving a lot and generating a lot of warmth, you could start to overheat. And when you stop moving, all that moisture will eventually cool down, making you much colder. All this to say: ventilation is vital.

Trapping warm air

When you’re preparing to endure low temperatures, it can be tempting to don layer after layer, imagining that the more clothes you wear, the warmer you’ll be. But (as I can attest, after shivering through a day in South Dakota despite wearing everything from my suitcase), that’s not always true. Technically, what really determines how comfortable you’ll be isn’t the layers you wear, but what they’re made of, and what’s between them.

“Fundamentally, what keeps you warm is air,” explains Michael Cattanach, global product director for Polartec, a Massachusetts-based company that makes synthetic thermal fabric for outdoor apparel. “It’s about keeping pockets of air next to your body and using fabrics that trap air and keep layers of air together.”

“Fundamentally, what keeps you warm is air.”

Remember, your body is constantly giving off heat. When you wear clothes that trap still air (but not moisture) against your skin, the air absorbs that heat and you stay warmer. Leggings with a thermal grid pattern, for example, leave more room for air than something like skin-tight spandex, and will therefore keep you warmer. And heated air will remain around your body much longer if you insulate. Just like the insulation we use in our houses prevents heat loss, your clothing creates a barrier that keeps heat from escaping.

The art of layering is about quality, not quantity

Cattanach’s formula for a foolproof clothing system includes three layers: “something next to the skin to manage sweat and moisture, a second layer that’s insulating, then something with weather protection on the surface.”

The base layer is arguably the most important of the three, and should be fitted but not constricting. If you think you may break a sweat, or plan to be sitting by a fire that may eventually make you overly warm, for instance, go for a fabric that’s moisture-wicking; synthetics and synthetic/natural blends are a good choice.

“[Wool] is the original smart fiber, and can absorb and release moisture. Since basically the beginning of time, it’s existed to keep a mammal warm, cool, safe and comfortable.”

In terms of all-natural fibers, cotton is comfortable as long as your skin stays dry, but won’t do you any favors once you sweat and create moisture. Wool, on the other hand, can keep you warm even if you sweat a bit, and release that moisture to prevent overheating.

“It’s the original smart fiber, and can absorb and release moisture. Since basically the beginning of time, it’s existed to keep a mammal warm, cool, safe and comfortable”, says Clara Parkes, the New York Times bestselling author of Knitlandia and Vanishing Fleece. She points out that we’re mammals, too, so wool’s a natural choice to keep us warm. A thin and soft Merino wool base layer can help keep you comfortable without overheating, and a thicker wool sweater on top will let you use the principle of trapped air to your advantage.

“Wool is great for insulation because each fiber can have 18 or 20 curvatures per inch,” Parkes explains. “They’re like coiled springs, always pushing away from one another and creating space. The thicker the coils, the more still air is trapped in the fabric, and the higher its insulation abilities will be.”

Thick, rough sweaters are especially warm because the fibers are “jumbled and chaotic,” holding lots of air, says Parkes. For a less prickly layer against your skin, Merino works well because it’s a high-curvature fiber, trapping a disproportionate amount of air, despite its thinness.

The potential drawbacks to wool — and the reasons many lean toward newer, synthetic fleeces — are that it’s heavy and daunting to wash. But the latter shouldn’t stop you from buying that impossibly warm sweater, says Parkes.

“If you’re at all nervous about it, just do a hand wash, and treat it like you would your hair,” she says. “It’s chemically identical. A sink full of warm water, a quick dip, and an air dry is all it takes.”

What you do matters almost as much as what you wear

I called this a guide for staying warm while enjoying backyard beers, but actually, when it comes to staying warm, an alcoholic beverage can work against you.

“One of the most profound systems we have for heat loss or conservation is the simple dilation and constriction of our skin,” says Minson. When you’re cold, the skin constricts, sending blood flow back toward the core. When you’re hot, blood vessels just under the skin dilate, releasing heat. Unfortunately, alcohol is a vasodilator. When you first start to drink, you may feel warmer thanks to the blood rising to the surface. But it won’t last long — all that escaping heat through conduction and convection will cool you off quick.

That’s not to say your choices are to abstain or freeze — but if you’re going to be drinking, try to make up for that heat loss by raising your metabolic rate.

“Move a little more,” says Minson. “If you start feeling cold, just get up and do some squats. You may look ridiculous, but you’ll stay warmer.” The other thing you can do to hack your metabolic rate is with what you eat and drink, Minson adds. “More protein and fats will raise your metabolic rate.” In other words, don’t skimp on the charcuterie.

You can train your brain to tolerate the cold

Thermoregulation is a physical science, but there’s a major psychological component to staying warm, too. Humans are super adaptable creatures, and as the winter wears on, we really do grow accustomed to being cold.

“In November when it’s 42 degrees outside, you’re going to feel chilly because you’re not used to it,” Minson says. “When March rolls around, you’re used to it. It might be the same temperature, but your brain adapts.” Hence my misery during that South Dakota September snow: My brain wasn’t in winter mode yet.

You can make that adaptation happen sooner, he adds, through what basically amounts to exposure therapy. Bundle up a little less than you think you really need to, and force yourself to power through the discomfort. A caveat: No one’s suggesting you go out and get frostbite in the name of brain hacking. If you start to shiver, your core temperature is actually dropping and it’s time to add another layer. If you can’t get back up to feeling comfortable fairly quickly, it’s probably time to dissolve the hangout and call it a night.

But within reason, Minson says, it’s okay to embrace the cold. “It’s about being in a cold environment and being like, ‘Okay, I’m aware of the cold but I don’t feel cold.’ It’s losing the fear and realizing you can handle it. We really can hack our brains and feel more comfortable in the cold.”

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