Stanford researchers develop double-duty textile to keep warm or cool

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Researchers from Stanford University, California, have developed double-duty, reversible fabric that can keep one’s body both cool and warm, depending which side faces out, said a press release. A paper published November 10 in Science Advances, a team led by Yi Cui, professor of materials science and engineering, showed this innovation. The innovation allows clothes made from this fabric to keep the body at a comfortable temperature, irrespective of the weather outside.

The material was conceptualized as an energy efficient way to regulate body temperature. Temperature regulating devices consume a lot of electricity, which puts an increased stress on natural resources for energy production.

“Why do you need to cool and heat the whole building? Why don’t you cool and heat individual people?” asked Yi Cui.

Figure: A new textile made from a reversible fabric could warm or cool wearers and keep them comfortable. (Credit Yi Cui Group)
Figure: A new textile made from a reversible fabric could warm or cool wearers and keep them comfortable. (Credit Yi Cui Group)

The paper said, thirteen percent (13%) of all of the energy consumed in the United States is simply dedicated to indoor temperature control. But for every 1 degree Celsius (1.8 degrees Fahrenheit) that a thermostat is turned down, a building can save a whopping ten percent (10%) of its heating energy, and the reverse is true for cooling. Adjusting temperature controls by just a few degrees has major effects on energy consumption. Even in other parts of the world, temperature regulation is crucial to survival.

Clothing has been the traditional way of regulating body temperatures outdoors, where artificial temperature regulators do not exist. But, existing fabrics have obtuse properties. A particular fabric can be used for one purpose only. Cotton is a good material to cool the body down, while wool warms the body up. These properties cannot be manipulated.

According to the release, in 2016, the team announced a first step toward a solution: fabric that allowed the body’s heat to pass through, cooling the skin. The team used infrared radiation emitted by the body to develop the bilayer material. The radiation emitted by the body accounts for 40-60 percent of human heat loss. The team created a material that either insulated it or lets it escape.

According to the study, the material comprises a micrometre-scale sheet of carbon, which emits radiation effectively, coupled with a copper layer that helps trap the heat. Both sides of this bilayer are covered with a breathable polymer nanoporous polyethylene, which is transparent, allows infrared radiation to pass through and has a cooling effect. The thickness of the polymer layer above the copper is kept at only half the thickness as the layer covering the carbon sheet.

The press release said, “One side, a copper coating traps heat between a polyethylene layer and the skin; on the other, a carbon coating releases heat under another layer of polyethylene. Worn with the copper layer facing out, the material traps heat and warms the skin on cool days. With the carbon layer facing out, it releases heat, keeping the wearer cool.”

Studies with a synthetic skin sample showed the material can increase a person’s range of comfortable temperatures over 10 F. Postdoctoral fellow Po-Chun Hsu said in the release the potential range is much larger — close to 25 F. If all inhabitants wear a temperature regulatory textile, some buildings might never need air conditioning or central heating at all, he added.

“From my perspective, this work really highlights the significant opportunities in combining thermal engineering concepts with nanophotonic structures for creating novel functionalities,” said Shanhui Fan, a professor of electrical engineering who participated in the work.

The team will have to now make this technology into a fiber-like structure so it can be woven into clothing that look and function like traditional clothes. “Ideally, when we get to the stuff you want to wear on skin, we’ll need to make it into a fiber woven structure,” Yi Cui was quoted as saying in the press release by Stanford University.

The team has already started testing to make sure the fabric is machine washable with ambitions to create an easily manufactured, practical textile that people could use to save huge amounts of energy around the world. And they don’t stop there — Cui, Hsu and Fan envision clothing with medical devices and even entertainment printed right into the fabric.

“I think we are only seeing the beginning of many creative ideas that can come out of such combinations,” quoting Fan the press release said.

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