Heat energy can move in three ways: through conduction, whereby the atoms in materials pass energy to each other; convection, whereby high-energy atoms move through the environment; and radiation, whereby heat energy moves as electromagnetic waves. Clothing can control heat by changing how much radiation it allows to escape the body or how easily air can circulate.
Alon Gorodetsky’s team at the University of California, Irvine, is aiming to control radiative heat. “We’re drawing inspiration from squid, from cephalopods, that can do these amazing camouflage displays,” he says.
Squid can modify how they reflect visible wavelengths of light, using a cocktail of proteins in their skin. The team is adapting the technique to longer, infrared wavelengths that carry heat. “We are leveraging that for materials that can regulate the thermal emissions of an object,” says Gorodetsky, who won’t yet reveal how his team implements cephalopod-like radiation control. His team is partnering with US firm Under Armour, which makes base layers for sports clothing.
Tube system
Jintu Fan’s team at Cornell University in Ithaca, New York, is taking a different approach by controlling the circulation of warm and cold air through a network of miniscule tubes embedded in an undershirt. “On top, you can wear whatever you want to,” says Fan.
Temperature sensors in the vest monitor the skin, pumping in warm or cool air as required. “It’s like a mini air-conditioning system, but next to your body,” says Fan.
An alternative approach is to augment the body’s own ability to shed heat. To do this, Roy Kornbluh and his colleagues at non-profit research company SRI International are focusing on the body’s glabrous, or hairless, areas. In mammals, these areas act like a car radiator, helping heat escape from the body. In humans, the palms of the hands and soles of the feet are particularly important. “These tissues are the body’s radiator,” says Kornbluh. “We’re just augmenting it.”
Based in Menlo Park, California, his team is building prototype shoes that incorporate a heat pump made from a kind of plastic which is very good at transferring heat. This allows them to pull heat out of the body through the sole of the foot when it’s hot, and to push heat in when it’s cold.
“We believe we can make something that’s relatively unobtrusive – you might not even notice that it’s a special shoe,” says Kornbluh. “Hopefully, within a couple of months we’ll have our first visual prototypes out.”
Everyday wear
Clothing that controls heat is not new. But up to now, it has only appeared in bulky or uncomfortable garments for the military, aerospace and emergency services, or in lab experiments. Astronauts wear a temperature-regulating suit inside their spacesuits that uses liquid to move heat around – but this is heavy. ARPA-E has invested $30 million to make systems that are comfortable to wear in everyday life.
There’s a bigger picture to clothing that adapts to keep us comfortable – it has the potential to save huge amounts of energy. Keeping office temperatures within a tight range creates a big demand on resources, with air-conditioning systems accounting for 13 per cent of energy used in the US. Clothes that can adapt and keep us comfortable would allow that control to be loosened.
“If you can expand that temperature band by a couple of degrees in each direction and people wear clothing that controls comfort on the individual, you can save 1 or 2 per cent of all energy in the US,” says Gorodetsky. “That’s a huge number. Even a tiny fraction of that would be huge.”
“ARPA-E wants to reduce energy usage in the US – that only works if a lot of people are wearing these,” says Kornbluh. “We want everyone to be able to wear these, just like you have a smartphone with you.”
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