Researchers have detailed a new wearable fabric that can help urban residents survive the worst impacts of massive heat caused by global climate change, with applications in clothing, building and car design, and food storage.
- In tests under the sun in Arizona (US), the material kept 2.3 degrees Celsius cooler than the broadband emitter fabric used for outdoor endurance sports and 8.9 degrees Celsius cooler than the commercialised silk commonly used for shirts, dresses and other summer clothing.
- This, the researchers believe, will help many avoid the heat-related hospitalisations and deaths seen across the world this year alone. The textile has received a provisional patent.
- The findings have been revealed in a paper published in Science by researchers from the UChicago Pritzker School of Molecular Engineering (PME).
THE CONTEXT: Existing cooling fabric for outdoor sports works by reflecting the sun's light in a diffuse pattern so it doesn't blind onlookers. But in an urban heat island, the sun is only one source of heat. While the sun bakes from above, thermal radiation emitted from buildings and pavements blast city-dwellers with blistering heat from the sides and below.
- This means many materials that perform well in lab tests won't help city-dwellers in Southeast Asia and China when predicted massive heatwaves hits them over the next few weeks.
- People normally focus on the performance or the material design of cooling textiles. To make a textile that has the potential to apply to real life, one has to consider the environment.
- One simple example of considering the environment is that people stand most of the time. They wear materials designed to reflect direct sunlight, but only their hats, shoulder coverings and the tops of their shoes—about 3% of their clothing—face that direct light. The other 97% of their clothes are being heated by the thermal radiation coming at them from the sides and below, which broadband emitter fabric does not fight.
- The sun and sidewalks cook with different heats. Creating one material capable of protecting wearers from both provided a major engineering challenge for the team.
THE PROJECT: The PME team's new textile can help provide a passive cooling system that can supplement and reduce the need for energy- and cost-intensive systems.
- A thicker version of the fabric protected by an invisible layer of polyethylene could be used on the sides of buildings or cars, lowering internal temperatures and reducing the cost and carbon impact of air conditioning.
- Similarly, the material could be used to transport and store milk and other foods that would otherwise spoil in the heat, cutting refrigeration's impact.
HEAT WAVE: This year has already seen massive heatwaves around the globe, with cities in Mexico, India, Pakistan and Oman hitting temperatures near or past 50 degrees Celsius (122 degrees Fahrenheit).
- As global temperatures and urban populations rise, the world's cities have become "urban heat islands," with tight-packed conditions and thermal radiation emitting from pavements and skyscrapers trapping and magnifying these temperatures. With 68% of all people predicted to live in cities by 2050, this is a growing, deadly problem.
What they said:
Solar is visible light, thermal radiation is infrared, so they have different wavelengths. That means you need to have a material that has two optical properties at the same time. That's very challenging to do. You need to play with material science to engineer and tune the material to give you different resonances at different wavelengths.
— Chenxi Sui (Co-First Author)
PhD candidate
UChicago Pritzker School of Molecular Engineering
