Smart clothing opens cooling vents when wearer gets hot

By Stephen Beech via SWNS

The latest 'smart' clothing recognizes when the wearer is too hot - and opens tiny vents to allow them to cool down.

The new lightweight material traps thermal energy when dry, but opens a series of tiny vents to let heat escape when a person starts sweating.

The vents close again to retain heat once they are dry, explained the American scientists who developed the pioneering material.

They say it is 16 percent warmer than traditional textiles when dry with the flaps closed and 14 percent cooler when humid with the flaps open.

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 scenarios.

Dr. Po-Chun Hsu, Assistant Professor of mechanical engineering and materials science at Duke University, said: “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.

“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. And he knew that if cut into flaps, nylon curls in on itself a little bit when one side is exposed to moisture.

However, nylon is not known for making 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 a 'Goldilocks' spot 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 interfering with the vents opening.

Puzzled as to what exactly was happening, Dr. Hsu turned to Duke colleague Professor Cate Brinson. Working with her graduate student, Boran Ma, Prof Brinson was able to provide an explanation.

Prof Brinson said: “It’s surprising and counterintuitive, but adding something heavy on top of a polymer can actually make it bend and open more.

“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 millimeters long - about the size of a fingernail.

Dr. Hsu said: "Compared with an average traditional textile represented by a blend of polyester and spandex, the material is about 16 percent warmer when dry with the flaps closed and 14 percent cooler when humid with the flaps open.

"Put together, the nylon-silver hybrid can expand the thermal comfort zone by 30 percent."

He says the approach has advantages to existing methods of venting heat through warm clothing, such as placing zippers beneath the armpits.

Dr Hsu said: “We want the sweating parts of the body to be vented, which is not necessarily the underarms.

“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 color without changing its thermal attributes.

Dr. Hsu added: “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.

“With enough work, this kind of material could look very similar to what we’re wearing today.”