The Science of How Certain Fabrics Keep You Warm

Find out which cold weather fabrics to reach for to fend off the chill—and why.

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| February 19th, 2013

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Remember how wetness makes any temperature seem more extreme? When cotton holds onto moisture, Beechinor explains, not only does it make you feel gross and wet, but it can also amplify your own body heat. “If you are wearing cotton as a base layer,” he says, “any strenuous activity will cause perspiration and that sweat will be absorbed by the cotton against your skin.” Your sweat on the cotton then pulls heat away from your body, making you chilly.

Nylon may seem like an obvious layering choice, as you might consider wearing tights under your pants to add a slim second layer. But Gray doesn't recommend that strategy. “Nylon will freeze you,” he says. “It's high thermal conductivity and it has big moisture regain.” That means it eagerly draws away your body heat and will stay wet for a long time. Rayon has similarly undesirable qualities.

Protecting Yourself From the Elements
If you need to be out in wet weather for an extended period of time, look for a waterproof, breathable shell. Gray explains that “breathable” waterproof clothing does not actually allow air to pass back and forth. “What it's letting out is water vapor.” he says. “Most waterproof breathables have no air permeability at all, so there is no real air exchange between the inside and the outside.” Instead, he explains, it's a chemical exchange—liquid moisture inside your clothing can escape in a vaporous state.

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Faced with windy rather than wet weather? There’s a reason why windy days can leave you feeling chilled to the bone. “Wind scrubs the warm boundary layer from around our bodies, making it colder,” says Gray. It causes the moisture on your skin to evaporate and that evaporation cools you down.

Fortunately, Gray adds that almost all breathable waterproof fabrics are also windproof. Athletic wind shell jackets are a great choice for gusty days. Just be sure your clothing forms a tight seal around your neck, wrists and pants hem since these are areas where wind can enter, forcing warmer air out.

Finding outdoor clothing that fits you properly has other benefits. “Tighter clothes that are closer to the skin will allow for better wicking away from your body,” explains Beechinor. That means they’ll allow excess sweat to transfer from you to the garment and then evaporate. But if your clothes are too tight, they can block blood from circulating through your body, a quick path to frostbite.

In general, it’s about the layers. “Most people find the traditional layering system works,” Gray describes, “An outer rain shell, a mid layer that's insulative and a base layer that's wicking.”

Particularly prone to the cold? Slip on a lightweight, breathable windshirt after your base layer and before the outer layers. This will prevent cold moisture from building up beneath your clothes—and keep you nice and toasty.

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