Researchers in Belgium have unveiled the design for a fabric that could keep a person warm when worn one way, while cooling them down if worn inside out. Through simulations, Muluneh Abebe and colleagues at the University of Mons showed how the infrared-emitting properties of their “Janus textile” could allow it to be comfortably worn across a temperature range of 13°C. Although large-scale manufacturing of the material is not yet feasible, the researchers hope their results will inspire further research into similar fabrics.
When at rest in indoor environments, about half of the heat lost by our bodies is transferred to the surrounding air through conduction and convection. To stay warm, we can simply slow these processes by adding layers of clothing. However, the other 50% of heat loss at rest occurs via infrared radiation from skin and from the surfaces of clothing. Therefore reducing this radiative loss – or increasing it to improve cooling – involves modifying the surfaces of clothing.
In previous studies, researchers have shown that some materials can absorb infrared radiation from the wearer’s skin, and then allow it to escape from a highly emissive outer surface. The effect of this is to cool the wearer in warm environments.
Photonic engineered textiles
So far, however, these cooling fabrics have largely been composed of impermeable membranes that trap air and humidity against the skin, making them uncomfortable to wear. To address this issue, Abebe’s team turned to the advanced capabilities of photonic engineered textiles. These involve the of integration infrared-emitting and absorbing elements into mechanically flexible fabrics.
In their study, the researchers present a theoretical design for a 20 µm thick Janus textile – named after the two-faced Roman god. The two interwoven sides of the material are composed of two different fibres – dielectric and metallic – each with very different infrared-emitting properties. On one side the dielectric fibres can emit large amounts of radiation; while on the other side the metallic fibres have low emissivity.
Textile gates infrared radiation to keep cool
To test their asymmetrical fabric, the team used a thermal model to calculate the differences between the infrared transmission, reflection, and absorption properties of each side. They discovered that if the Janus textile is worn with its dielectric fibres touching the skin, large amounts of radiation could be prevented from escaping – keeping the wearer comfortably warm in temperatures as low as 11°C. Yet if the fabric is flipped inside-out, it could emit as much radiation as bare skin – keeping the wearer cool in temperatures as high as 24°C.
On top of these passive heating and cooling capabilities, the Janus textile is thin and flexible. Gaps between the fibres should allow moisture to move away from the body – ensuring comfort for the wearer. For now, Abebe’s team acknowledges that high manufacturing costs will mean that such reversible fabrics will not be appearing in our clothes any time soon – but with further research, they hope that new designs could keep us comfortable across a wide range of temperatures.
The research is described in Physical Review Applied.
