Por: Admin
mar 28, 2025
Ideas
New fabric that favors heat exchange between the body and the environment can keep people more comfortable in the summer
The skin is the main thermoregulatory organ of the human body, and clothing acts as a thermal resistance interposed between the body and the environment, representing a barrier to heat exchange by convection. Its resistance depends on the type of fabric, the fiber, and the fit to the body. It is measured through selective dry exchanges relative to the user, and its unit of measurement is known as clo (from the English term clothes).
Thermal comfort is defined as the mental state that expresses a person's satisfaction with the environment that surrounds him – and is a very important factor when considering the energy efficiency of buildings. Comfort variables are divided into environmental and human variables: temperature, mean radiant temperature, speed and relative humidity make up the environmental variables, while metabolism generated by physical activity and the thermal resistance offered by clothing are human variables.
If a room is cold, you have a few options: you can choose to put on a warmer shirt or turn on the heater. If the room is hot, however, the choice is not so simple. There is a limit to how much clothing we can take off in the workplace, and wearing some lighter items, such as T-shirts, is frowned upon in some business circles. The default solution, therefore, is to turn on the air conditioning.
Fortunately, our adaptation to warmer temperatures may change if a discovery published in the journal Science this week is put on the market. Yi Cui and his colleagues at Stanford University have discovered a fabric that keeps the skin 2°C cooler than a cotton garment.
In terms of comfort, this is a significant reduction – which could be good not only for the user but also for the energy bill. If the new fabric were to become widely adopted, environments could be kept warmer than they are today, saving huge amounts of energy in the summer months.
The goal of Dr. Cui’s research was initially to lower people’s temperatures by adjusting the way heat radiates from their bodies. More than half of body temperature is in the infrared part of the electromagnetic spectrum. This means that the wavelength is longer than the wavelength of visible light.
Materials such as polyethylene allow both wavelengths to pass through, and are therefore useless for weaving clothes – they let both light and heat through and do not protect us from cold or nakedness. In contrast, fabrics such as wool, cotton and silk do not allow either wavelength to pass through, thus trapping infrared and keeping us warm.
The answer to Cui’s investigations came from research into batteries. A material commonly used in modern batteries is called nanoPE. It is a type of polyethylene perforated with pores measuring 50 to 1,000 nanometers (billionths of a meter). These pores are used to regulate the flow of ions inside the battery – and they are just the right size to make the material opaque to visible light. However, these pores cannot affect the infrared part of the electromagnetic spectrum, blocking less than 10% of infrared rays.
When fresh from the factory, nanoPE resembles a plastic sheet and is not very comfortable to wear. To get around this, the Stanford team made three changes. First, they punctured the sheet at regular intervals with a small needle, to allow air to flow in and out. Then, they added a substance called polydopamine, which makes the plastic more hydrophilic. This means that instead of repelling sweat and causing it to clump on the skin, the modified nanoPE absorbs perspiration and carries it to the outer surface of the fabric, where the sweat evaporates. Ultimately, to increase the material’s mechanical properties, the final product was made up of two sheets of nanoPE separated by a widely spaced cotton mesh.
The team then tested how the added material affected the performance of the nanoPE. In a room at 23.5°C, the temperature of bare skin was 33.5°C. Skin covered in cotton fabric was 37°C, while skin covered in nanoPE alone was 34.3°C. Variations with perforations, mesh and other modifications did not perform as well in thermal performance, but they still reduced skin temperature by at least 2°C compared to cotton.
Of course, designers won’t be the first to rush out and create fashion models with the new fabric, but the discovery has created a new way of thinking about reducing body temperature. Manipulating the waves emitted by the human body through fabrics is clearly an idea that works. In addition to being used indoors, Dr. Cui's new fabric has several applications outdoors – after all, there is no air conditioning in deserts, and people who work there, such as soldiers, probably care very little about fashion. The next steps would then be to find materials that perform the task in a more comfortable way for the user than nanoPE.
Source: The Economist