Scientists have created a line of smart clothing that recognises when you're too hot and opens tiny vents to cool you down.
Anyone who is old enough to have owned a Global Hypercolor T-shirt back in the 90s is likely getting strong deja vu vibes right about now.
Back then the viral brand created a range of T-shirts that changed colour in reaction to spikes in the wearer's body temperature.
Despite it seeming somewhat weird to wear a shirt that changes colour as you sweat they literally flew off the shelves.
Fast forward almost thirty years and it seems fashion and science are once again colliding to experiment with heat-triggering materials, this time to effectively prevent your T-shirt changing colour when you're hot.
The latest 'smart' clothing uses a new lightweight material which traps thermal energy when dry, but opens a series of tiny vents to let heat escape when a person starts sweating.
The vents then close again to retain heat once they are dry, the scientists who developed the pioneering material explain in the journal Science Advances.
As well as keeping you 15% cooler with the vents open, the new clothing is 16% warmer than traditional textiles when dry with the flaps closed.
Using physics rather than electronics to open the vents, the research team say that the innovative material has potential as a patch on various types of clothing to help keep the wearer comfortable in various conditions.
“People who are skiing or hiking in colder weather usually wear layers so they can adjust how much heat their clothing is trapping as their body heats up," explains Dr Po-Chun Hsu, Assistant Professor of mechanical engineering and materials science at Duke University.
“But by strategically placing patches of a material that can let out heat when a person is sweating, one could imagine making a one-piece-fits-all textile.”
When first attempting to make such a dual-purpose material, Dr Hsu turned to nylon as it's inexpensive, lightweight and soft.
He also knew that if cut into flaps, nylon curls in on itself a little bit when one side is exposed to moisture.
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However, nylon doesn't make particularly warm clothing. So Dr Hsu added a layer of heat-trapping silver on top.
Expecting the weight of the silver to bog down the nylon flaps, he tried to make the layer as thin as possible, but to his surprise the silver addition actually made the flaps curl back even more.
After experimenting with various thicknesses of silver, Dr Hsu discovered what he describes as a 'Goldilocks' thickness around 50 nanometres - 2,000 times thinner than a sheet of paper.
Any thinner and the phenomena wouldn’t be as strong. Any thicker and the weight of the silver started interferring with the vents opening.
Dr Hsu turned to his colleague Professor Cate Brinson and her graduate student, Boran Ma, Prof Brinson was able to provide an explanation about why the combination of materials seemed to work.
“It’s surprising and counterintuitive, but adding something heavy on top of a polymer can actually make it bend and open more," Prof Brinson explains.
“What it comes down to is that the silver is shrinking and the nylon is expanding.”
Prof Brinson explained that when the bottom layer of nylon gets wet, it wants to expand like a sheet being pulled from its sides, but because it’s attached to the silver on top, it can’t stretch in those directions.
She said the easiest option remaining is for the two-layer material to curl up, allowing the nylon to expand while forcing the silver to shrink.
In the experiments, the researchers created a patch about the size of a human hand with flaps a few millimetres long - about the size of a fingernail.
"Compared with an average traditional textile represented by a blend of polyester and spandex, the material is about 16% warmer when dry with the flaps closed and 14% cooler when humid with the flaps open," Dr Hsu adds.
"Put together, the nylon-silver hybrid can expand the thermal comfort zone by 30%."
He says the approach has advantages to existing methods of venting heat through warm clothing, such as placing zippers beneath the armpits.
“We want the sweating parts of the body to be vented, which is not necessarily the underarms," he explains.
“Our chest and back need more venting, but the effort to unzip these areas, if zippers are even available, is almost the same as simply taking off the clothing.”
Now, Dr Hsu is working on making the vents as small as possible while retaining their effectiveness.
He’s also exploring using a top nanocomposite layer that could make the material any colour without changing its thermal attributes.
“I expect that if we can find the right laser cutting method to create very small flaps and attach the patch to clothing, we can create this effect without looking like we’re wearing a costume," Dr Hsu adds.
“With enough work, this kind of material could look very similar to what we’re wearing today.”