Unfortunately, that's not quite suitable for the extreme cold that soldiers and outdoor enthusiasts often must endure for extended periods.
The solution: a new generation of high-tech jackets that create their own warmth, powered by lightweight lithium batteries.
The jackets jettison the electric blanket model traditional wires running through cloth to produce heat. Instead, they conduct heat through stainless steel microfibers thinner than a human hair. The fibers are as washable, bendable and soft as the fabric into which they're woven.
Malden Mills of Lawrence, which makes Polartec fleeces, has licensed the technology to The North Face, which is using it for the high-end MET5 jacket, and to Land's End for a blanket.
The North Face jacket doesn't look unusual. But its vest lining heats to 114 degrees on full power, doubling its warming effectiveness.
Down the road, fibers could relay not only heat but also data, turning clothing into truly wearable computers something scientists have experimented with for years but haven't perfected for widespread use.
Someday, the technology could even turn strangely back on itself: air-conditioned textiles to keep the users cool.
Malden Mills is banking on heating technology to help pull it out of financial difficulties. Six years after a devastating fire, it filed for voluntary bankruptcy protection in December.
"Part of our DNA here is, you innovate or you die, especially in this industry in the U.S.," spokesman David Costello said.
Until production costs fall, The North Face and Malden Mills say wired textiles are likely bound for a niche market. "Think about photographers, policemen, construction workers, the military," Costello said.
The military has already sent a lot of business to Malden Mills with nudging from the state's congressional delegation. The Pentagon has a $17 million contract to buy Malden Mills brand Polartec fleeces and jackets, and now it, too, is working on a number of electronic textile projects at its lab in Natick and elsewhere.
The Army's Special Operations Command plans to begin testing heated jackets soon, Malden Mills says.
"Textiles generally speaking have been a very conservative industry, and the electronics industry has been very cutting edge," said Carole Winterhalter, the lead textile technologist at the lab. "And we've been working to bring these two together to get mutual benefits."
After several patents and about four years of research, Malden Mills claims it finally perfected the tiny cables, making them thin enough to behave like textiles but here's the trick tough enough to survive industrial weaving.
The jacket sold by The North Face has two settings: Medium heats the fabric around the chest area up to 108 degrees for five hours. High goes to 114 degrees for 2 1/2 hours.
"It's on yur chest because you want to heat up the core where the heart and lungs are," says Costello, who spent several 85-degree August days testing the technology in a frozen Massachusetts fish locker. "If the core is warm, where all the blood circulates through, then your extremities are fine."
The North Face has done its own testing, sending teams of climbers and extreme athletes on wilderness expeditions.
The company even dropped one climber in a 20-foot crevasse and buried him in snow until he started shaking, then had him flip on the jacket.
"Soon afterwards he stopped shaking, and we realized this was a pretty cool project," said Thomas Laakso, advanced project manager at The North Face, the San Leandro, Calif.-based unit of VF Corp.
A new version and a vest will be out in the fall.
The company claims MET5 has been a big hit, despite a $500 price tag, during an initial limited release, though it declined to provide sales figures. It says it received requests for the jackets from several Winter Olympians.
In the works for Malden Mills are gloves and, further down the road, jackets that carry not only heat but data, monitoring heart rates and body temperatures, for instance.
"The thing that is holding it back now is the battery technology," Costello said. That's a common obstacle for many portable electronics, from laptops to cell phones.
The military is nevertheless pushing hard, hoping to put sophisticated electronics and optics into clothes in three to five years.
"These guys had the most tragically out of date you wouldn't believe clothing up until about two years ago," Costello says.
Winterhalter, of the Army's Natick Lab, doesn't dispute that, but says there has been progress.
Natick has already tested a textile USB cable that meets the performance standards of a standard cable and, just as importantly, the standards of wear-and-tear that a textile is expected to meet.
"We can launder it, bend it, stitch it down to your uniform, we can integrate it through various layers of the uniform system," Winterhalter says. "It's not going to be a snag-hazard like some of these off-the-shelf cables will be."
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