Scientists give new meaning to the phrase ‘cool clothes’

Scientists give new meaning to the phrase 'cool clothes'

Researchers have developed a fabric that can keep skin nearly three degrees cooler than cotton.

Scientists are taking a close look at the cooling power of polyethylene, the most common plastic on Earth and the essence of plastic bags, bottles and wrapping. In fact, their research found that a person wearing material incorporating polyethylene would definitely feel cooler than someone wearing cotton clothing.

Why? Well, it has to do with the material’s ability to allow infrared radiation to pass through it. That’s what our bodies produce when they throw off heat. It’s the thermal radiation that makes us visible in the dark to someone wearing night-vision goggles.

In fact, roughly half our body heat is dissipated as infrared radiation, even when we’re just sitting in an office. But if that radiation is trapped, we feel warmer. And, just about all clothes are opaque to infrared. That’s not true of polyethylene—its simple chemical bonds keep it from absorbing that radiation.

“The textile industry hasn’t paid much attention to the infrared radiation property of clothing,” says Po-Chun Hsu, one of the Stanford researchers. “Specifically, transparency of infrared is an idea that has received very little research.”

Fabric of the future?

It doesn’t take a scientist, though, to recognize the shortcomings of clear plastic as clothing. The obvious one is that it’s see-through. But it also doesn’t absorb moisture, which could result in some serious perspiration issues.

The Stanford researchers addressed the former by tracking down a version of polyethylene often used in batteries, one that is opaque to ordinary light, but not to infrared radiation. So, while it’s not transparent, it lets body heat pass through.

As for the moisture issue, the scientists were able to use chemicals to modify the material so it became hydrophilic, or more accommodating to liquid. Water can now spread across its surface instead of beading.

They also experimented with inserting a layer of cotton mesh between two sheets of modified polyethylene to give it more strength and structure. A swatch of that material and a piece of cotton fabric of similar thickness were both placed on a surface the temperature of bare skin. Then a comparison was made of how much heat was trapped. The cotton fabric was found to make the surface 3.6 degrees Fahrenheit warmer. That difference could be enough to keep someone wearing the new fabric from turning up the air conditioner, the researchers suggest.

That comparison seemed to confirm their belief that using a substance that permits a freer flow of infrared radiation, such as polyethylene, can help a person stay cooler. But Hsu acknowledged that the Stanford scientists are still in the early stages of finding the best way to incorporate the plastic material into clothing. It might be combined with more conventional fabrics. Or it might be possible to actually make polyethylene into a woven textile.

“That would make it feel more like clothes we wear,” he says. “We want to see if we can make it into more traditional cloth, with its softness and stretchability. We’re exploring all kinds of possibilities.”

Another approach

Researchers at MIT are also analyzing the potential of using polyethylene as a way to make it easier for body heat to escape. But they’re taking a somewhat different approach.

“We’re working from the bottom up,” says researcher Svetlana Boriskina, who explains that the MIT team is working at the microscopic level, focusing on determining the right thickness of fibers necessary to make a fabric transparent to infrared radiation. “The people at Stanford are taking the opposite approach—more from the top down” she says. “They started with a transparent sheet of plastic, but that’s not good for clothes. And they’ve modified it to make it better.”

Actually, Boriskina’s group is also working with polyethylene because of its unique properties when it comes to letting infrared radiation pass through it. Conventional fabrics, no matter how thin the fibers, will still capture that light and turn it into heat. Not the plastic.

“Infrared light can escape it,” she says. “The downside of polyethylene is comfort. Like if you touch it, does it feel good? This is the biggest challenge right now. Unless you can make it comfortable, who’s going to wear it? And, how strong can you make it? If you put it through several washing cycles, I’m not sure it will survive.

“But don’t get me wrong,” she adds. “What they’ve done at Stanford is a very important milestone. It’s the first experimental demonstration that this idea does work.”

While admitting that she may be overly optimistic, Boriskina thinks this type of clothing designed to keep people cool could be available in three to five years. She pointed out that the clothing industry now works with microfibers, so a process already exists. Manufacturers would need to do the same thing with polyethylene or another material that is infrared transparent.

How long this innovation takes to have an impact on energy savings is another matter, Boriskina suggests.

“In the short term, the biggest challenge is to make this clothing comfortable,” she says. “But in the long term, for real energy savings to occur, you would need to have a lot of people wearing this type of clothing. If too many people are still wearing conventional clothes, they may not want to turn down the air conditioner.”