You are not alone inside your clothes.
Something is in there with you, snuggling beside you, clinging to your every crannied nook.
Most of the time you don’t notice it, this companion that moves as you move. Its touch is as light as air.
In fact, it is air.
It’s your atmosphere, a blanket of wispy vapors held in and under your clothes. And that’s good, because it’s getting cold outside. If your clothes can cuddle air close and keep it still, you are much less likely to freeze to death outdoors.
But what are you doing outdoors ? Running, biking, riding your horse ? Are you on your duff watching the kids play soccer ?
The clothes that snuggle air while you’re sitting might lose it altogether should you jump up and gallumph about. Or, more likely, they might hold air too closely until you overheat and soak them with sweat.
And then you’d be wet and cold.
How can an active person avoid overdressing or underdressing ? All kinds of experts, including your mother, agree that such complicated times call for more than mere clothing; they call for clothing insulation systems. Experts have a term for such systems — no, not “CIS.” The word is “layers.”
Get too hot as the sun rises or after you run around — take off a layer. Get cold again, put that layer back on.
You already know this. Everybody already knows this. But everybody does not know as much about why layers do what they do as everybody thinks everybody knows.
Quick test: Are the following statements true or false ?
1. Thicker fabrics ban cold more effectively than thinner ones, so put on your thickest and bulkiest layer last.
2. More than half your body heat is always escaping through the head, so wear a hat.
3. Hands and feet suffer first when the body gets cold because their blood vessels contract, so you should wear extrathick layers around them.
4. There are Internet sites with tools that take the guesswork out of layering by prescribing right combinations for different temperatures; for instance, Runner’s World magazine has one for runners. Are your answers correct ? Read on to find out.
TRAPPED Fabric — thin, bulky, whatever — doesn’t keep you warm. You keep you warm; the fabric merely helps. “People need to realize that in a textile, the fibers are simply stabilizing air,” says Elizabeth Mc-Cullough, professor of textiles at Kansas State University in Manhattan, Kan. “It’s this trapped air that is providing insulation.” Your body heats the air around you all the time, when you’re toasty warm or even when you’re freezing to death. Why ? Because you make heat, you hot thing, you.
But air is like an ocean current, and the heat you make can flow away from you with it.
“It has to be still,” McCullough says. “That’s what the fibers do. The fibers immobilize the air. The little air molecules hang on to fiber surfaces. So you have air trapped inside fabrics and between fabrics.
“ That’s another reason why layering is efficient, because every time you add a layer of fabric you also add an air layer.”
Fabrics that trap air well have a thick and porous structure, like wool, feathery down or synthetic fiberfill, and a napped or pile surface, like knitted fleeces. (A woolly sweater. A fuzzy fleece jacket. )
But the pores that let air in also let it out, for instance, when the wind cuts right through your fat sweater.
“A sweater is really a very inefficient way of dressing... because they are very holey,” McCullough says. And fleeces are, too, unless they’re fabricated in layers that include one that blocks wind — for example, one of the new fluoropolymer “membranes” or “films.”
“If you’re going to wear your fleeces as your outside layer, and you want wind protection, you’ve got to have a film in there that will stop the wind from coming in,” she says.
In other words, statement No. 1 is false. Your outermost layer should block wind.
And also rain. Any water that flows through your insulating fabric will displace the air, and you’ll have a very hard time keeping that water warm enough to stay comfortable. Add wind to a wet body inside wet clothing and you get death from hypothermia.
Note that water also comes from within.
WET IS BAD It’s not just the heat, it’s the humidity. Your wonderful body passes water vapor and also liquid water — in its attempts to maintain the temperature of your brain and your innards. And this matters to people who exercise in the cold, because heat is released as a byproduct of the biochemical reactions that power muscle contractions. The harder and / or longer you exercise, the more that heat builds up, and sooner or later, your brain makes you sweat to help get rid of it. So the clothing that’s just right during the first half hour of your morning run might be sweaty for the last half hour. So you can take off a layer. But what if you’re skiing ? You can’t take off protective moisture-blocking layers when there’s a chance you could fall down in wet snow.
So when you plan to work out hard, think about what type of layer you want closest to your sweat-prone skin. Depending on the activity, maybe you want a sweat-management layer between you and your air-trapping stuff.
As Chris Townsend puts it in the second edition of The Backpacker’s Handbook (Ragged Mountain Press ), “the prime purpose of the inner, or base, layer is to keep the skin dry rather than warm. If perspiration is removed quickly from the skin’s surface, your outer layers keep you warm more easily. Conversely, if the layer of clothing next to your skin becomes saturated and dries slowly, your clothes, however good, have a hard time keeping you warm.
“ No fabric, whatever the claims made for it, is warm when wet.”
Townsend wrote that in 1997, and it’s still true, despite dramatic advances in performance fabrics. Wool remains the best insulator when wet, but wet wool is no joy. Newfangled “wicking” fabrics sold under brand names like Coolmax, Dri Fit, Dry Weave and Under Armour do transfer moisture better than older weaves — for instance, woven cotton undies. Wicking garments are sold in specialty sports stores and also in big-box chain stores. They’re not hard to find. But now we’re up to three potential layers. Might be enough, might be too much. Which it is depends on more than merely what kind of fancy “performance” fabrics you’re wearing.
FORCED EXHALATION McCullough is co-director of Kansas State’s Institute for Environmental Research, where she tests garments for companies like The North Face and L. L. Bean. Among the wondrous new moisture-management garments she tests are outer-layer shells that not only block wind and keep out rain but “breathe” to let the sweat that’s wicking through a base layer eventually evaporate away.
She says, yes, these waterproof fabrics (like Gore-Tex, eVent and other polytetrafluoroethylene, or PTFE, films ) will let sweat out, and they work very well during intense exercise... unless they can’t.
For these new garments to transfer your heat or your moisture to the environment, there has to be a significant difference between you and it to drive the process.
On average, body surface temperature is 95 degrees F. “As long as the environmental temperature is cooler, you will lose heat from your body’s surface to the environment,” she says.
And for water vapor to move, “you have to have a vapor-pressure gradient from your skin to the environment.” In other words, vapor pressure at your skin (your personal humidity ) has to exceed that in the environment — which it can’t if the environment is raining. So then you open zippers and try to ventilate. But even so, you’re bringing in moist air. “If it’s raining you’re kinda doomed,” she says.
THE CAPPER So we’ve mentioned a waterwicking base layer, an air-trapping warm layer and a wind- and / or rain-blocking-but-breathing shell. How should you disperse these layers over your body ? Is it smart to put extra layers on fingers and toes ? Can you really lock in half your heat with a hat ?
These questions have simple answers — but for complicated reasons. Take the hat thing.
The body responds to cold by shivering and by constricting blood vessels to the arms and legs. “But the blood vessels in the head don’t constrict, because your body’s priority is keeping the brain functioning,” McCullough says.
Does that mean the body loses most of its heat through the head ? It depends.
In the University of Arkansas Research Frontiers for fall 2008, kinesiology professor Barry Brown explains that, when the body is at rest, the rate of heat loss is pretty much equal for any exposed part of the body, including the head. The head makes up only 10 percent of body surface area, Brown notes, “so, at rest, heat loss through the head accounts for only 7 to 10 percent of total heat dissipation.”
But “as you begin exercise,” he writes, “cerebral blood flow increases due to increased cardiac output and the percentage of heat lost through the head accounts for about 50 percent of total body heat loss.”
As exercise continues, more blood is directed toward working muscles which begin to generate more heat. The skin arterioles expand, redirecting blood flow to the skin, and eventually you start to sweat.
“Hence, total blood flow to the brain is decreased, and the percentage of total body heat lost through the head is reduced to about 10 percent,” Brown writes. “The percent lost through the scalp returns to 7 percent after sweating begins.”
But Brown notes that while you’re shivering, “55 percent of the heat loss can occur in the scalp. Therefore, head covering during cold weather is strongly advised.”
McCullough says people perceive the hat as a magical garment because often that’s the last part they insulate. “If the head is the only area left uncovered, you can make a tremendous difference to your clothing insulation by simply adding a hat.”
And therefore, statement No. 2 is false. You aren’t always leaking half your heat from your scalp.
What about statement No. 3, the one about warming suffering fingers and toes with extra layers ? Those skinny digits have relatively little mass and a lot of skin area, which means they lose heat rapidly. And so, yes, it makes good sense to protect them.
But the root of their misery is that panicky constricted blood flow to the arms and legs. Get the rest of your body’s surface adequately insulated so those vessels can relax, and your hands and feet won’t suffer. Statement No. 3 is false.
McCullough says the most effective way to keep warm is to cover as much of the body’s surface as possible and to distribute the layers evenly over the body.
WHAT TO WEAR Considering that three of our four quiz questions proved false, smarter readers are already thinking that statement No. 4, the one about finding handy clothing prescriptions on Web sites is false, too. Oh, you’ll find plenty of advice, but it might or might not suit your body. “There’s no magic formula for that at all,” McCullough says. Figuring out how to layer your body for your activity in the conditions you’ll face takes trial and error. It helps to keep a log of what you wear, when you wear it and how it all works out. And to check the thermometer before you venture outside. But you knew that already.
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