WINTER Trying to stay warm? Don't sweat it but layer it

Wear something against your skin that pulls the moisture away.
KNIGHT RIDDER NEWSPAPERS
On a nose-nipping midwinter's day, staying warm has everything to do with staying dry.
That's why, when he's working or playing up there in Winnipeg, Manitoba, Gordon Giesbrecht is constantly zipping and unzipping. And putting on and taking off again.
"On a day when I'm being active, I might fine-tune the layers 10 times," said Giesbrecht, a professor of thermal physiology at the University of Manitoba, where he has plenty of opportunities to test his theories on staying warm in the cold.
All that clothes-arranging is in the interest of keeping sweat at bay because sweat, according to the cold-weather experts, opens the door between you, inside that fluffy down parka, and that brutal frigid air a few inches away.
Chilling out
Anytime you're in an environment that's cooler than 98.6 degrees, the air around you is trying to steal your warmth to level the thermal playing field. Nature likes a uniform temperature. On top of that heat loss from radiation, convection forces kick in if the air or water around you happens to be moving. When the wind blows, it displaces the warmed air from around your body, forcing your body to heat more air, which will in turn blow away.
"That's why wind chill is such an important thing," said Andy Bourne, an instructor and mountain-climbing expedition leader with the American Alpine Institute in Bellingham, Wash.
Add water to the mix, and the heat is moving around even faster. A drizzly 35 degrees feels colder than a dry 35 degrees because it really is siphoning off more of your hard-earned heat. Because of its greater density, water pulls heat from your body 25 times faster than air, Bourne said.
When you get cold, your body responds in two ways: It shivers, and it constricts blood vessels, especially those leading to the hands and feet. If your extremities are cold, Bourne said, the blood that circulates through them gets cold, too. When it returns to the critical organs like the heart and lungs, it's too cold for optimal functioning. So to keep the vital organs at the right temperature, the body ratchets down the amount of blood going to the chilly nether regions.
"It reduces it by a lot, actually," Bourne said. He said that, on average, between 300 and 500 milliliters of blood flow to the extremities each minute. When the hands or feet are extremely cold and on the verge of frostbite, blood flow is typically around 30 milliliters a minute.
So keeping the extremities warm can help keep the entire body warm, Bourne said.
The body's other cold-weather coping strategy is shivering. Without your giving it a thought, your muscles rapidly contract and relax, contract and relax in an attempt to generate heat. And, to an extent, bodies acclimate to cold, Giesbrecht said.
"If it's 38 degrees in November, you put all kinds of clothes on. If it's 38 at the end of March, you say, 'Oh, it's nice out.' You can see the difference in a week, even in a couple of days."
Giesbrecht, who plans to spend most of this month on a long-distance hike in preparation for a trek to the North Pole next winter, sometimes advises people to build their tolerance by underdressing for the conditions, although he recommends bringing along more clothes, just in case.
Layering
Under normal conditions, however, he's emphatic about the need to wear enough clothes and the right sort of clothes. Cold-weather specialists generally recommend many layers, including three types of fabrics. If you're likely to be working up a sweat, it's important to wear something against your skin that wicks, or pulls, moisture away. The idea, again, is to maximize the insulation value of your clothes by keeping yourself dry. Long underwear made of polypropylene, silk or Capilene is the best bet. The worst bet, because it sucks up water and retains it, is cotton.
"You want to stay away from cotton at all costs," Giesbrecht said. "We call that the death fiber."
On top of the wicking layer should be an insulating layer.
"Really all you need is something that traps dead air," Bourne said. "That trapped air forms the insulation."
There are many choices, including synthetics such as Polartec and PrimaLoft, which Bourne considers "the best of the synthetics."
There are natural fibers with a long history that serve quite well, too, he said.
"Wool does really good and definitely keeps you warm while it's wet. That's the original fleece."
As long as it's kept dry, down is hard to beat, Bourne said.
"Down has such a high loft factor. Over time, that isn't lost very much. It bounces back, better than the synthetics we've come up with. Over time, synthetics get bunched up. The problem with down is if it gets wet, it gets all clumped up and won't keep you dry. You have to be really careful not to get it wet."
Depending on what you're likely to encounter, the outer layer of your clothing should repel wind and water. Gore-Tex is the old standby, although "they've been improving on that idea for the last 10 years," Bourne said. A new introduction by a Swiss company known as Schoeller is stretchy and breathable, he said, but at a cost of less wind and water resistance.
It's always smart to have a hat or hood at the ready, Giesbrecht said, although he contends that heat loss through the head has been overstated. He says about 10 percent of body heat exits through the head, which accounts for about 6 percent to 8 percent of the body's surface area.
"People make too much a deal of this hat," he said.