A reversible fabric from Stanford University could warm up or cool down its wearers, depending on their preference – and which side of the material faces out.
At first glance, the invention resembles everyday kitchen wrap. The material, however, has more advanced capabilities than keeping sandwiches fresh.
On one half of the two-sided textile, a copper coating traps heat between a polyethylene layer and the skin; on the other, a carbon coating releases heat under an additional polyethylene sheet.
Worn with the copper layer facing out, the material warms the skin. In reverse, with the carbon layer on the outside, the fabric releases the heat, keeping the wearer cool.
Yi Cui, professor of materials science and engineering at Stanford, says the sandwiched material increases a person’s range of comfortable temperatures over 10°F. The lead researcher predicts an even greater temperature capability soon — one that, he envisions, could someday reduce a building's need for air conditioning or central heating.
After all, asked Cui, “Why do you need to cool and heat the whole building? Why don’t you cool and heat individual people?”
Cui spoke with Tech Briefs this week. His edited responses are below.
Tech Briefs: How did the double-sided fabric idea come about?
Professor Yi Cui: We first began working on radiative heating textiles and demonstrated the metallic nanowire textile in 2015. Then, in 2016, we switched to radiative cooling, using infrared-transparent nanoporous polyethylene.
Excited by the effect of radiation control and motivated by the huge impact on the environment and health, we engaged ourselves to explore more possibilities in this field. These previous works laid the foundation for us to generate the idea of a dual-mode textile.
Tech Briefs: How is it dual-mode? Specifically, how is the fabric able to both provide heating and cooling?
Cui: The carbon/copper bilayer is the key component providing the dual-mode capability. Carbon and copper have different radiative properties. When the carbon side faces outside, the carbon layer can help emit the thermal radiation and cool down the human body. If it becomes too cold, we can reverse the textile and let the copper side face outside; then, the thermal radiation will be reduced and warm up the human body.
Tech Briefs: What does the fabric look like?
Cui: The textile is smooth and sleek, mostly because it is currently a non-woven textile. We are developing the woven version, which is more common in everyday apparel. This dual-mode textile is composed of a copper/carbon bilayer sandwiched by nanoporous polyethylene.
Tech Briefs: What mechanisms are in place to make sure the wearer doesn’t get too hot or too cold?
Cui: The thickness of the clothing can be tailored toward the temperature range of environment. Together, with the human body's own temperature adjustment mechanism, it would work well.
Tech Briefs: What is most exciting to you about the possibilities of this kind of technology?
Cui: In the U.S., 12% of energy is spent on indoor temperature control. Our textile can help localize the thermal management around the human body, rather than constantly require the changing of the thermostat.
On the other hand, this textile potentially reduces the risk of temperature-induced illness such as strokes. Our experiment shows the dual-mode textile can expand the thermal comfort zone by 6.5 °C (11.7 °F) and help the wearer to adapt to wider temperature fluctuation. The numerical fitting result predicts 14.7 °C (26.5 °F) of comfort zone expansion with further optimization.
This technology can improve the building energy efficiency and personal health. It can also stimulate a more interesting and effective method for personal thermal management.
Tech Briefs: What’s needed to make this ready for wearables? Do you see people wearing this kind of fabric someday?
Cui: We are developing the fibers and the woven textile from this material, which will look and feel much more similar to the daily apparel. We believe thermal radiation and photonic control have a lot of potential and impact, and can fundamentally change the way we think about textile design, just like how wearable technology is rapidly reshaping our lifestyles.
What do you think? Will new fabrics reduce the need for central heating or air conditioning? Share your thoughts below.