I have terrible body temperature control. I stick my head in the freezer when it’s sizzling hot outside. Blood vessels in my hands spasm when it’s damp and chilly. “I’m hot; now I’m cold” is a running joke in my family.
But I’m lucky: Compared to cold-blooded animals, we humans have myriad ways of keeping our bodies humming along at a range of temperatures. We shiver when cold and sweat buckets to ward off heat. And when we struggle in extreme heat or cold, we have the brains to switch our wardrobe.
It sounds obvious, yet clothing has allowed us to explore the far reaches of our world while relatively comfortable and safe. But even the most technical garments—self-heating vests, Gore-Tex layers, or suits with built-in ice packs—have their limits. Most can either warm or cool the body—but not both—or require an external power source or a bulky battery pack.
These garments falter in desert or high-elevation areas, where temperatures can drastically swing from scorching heat to below freezing. And as we go beyond Earth, a lightweight suit that controls body temperature could make longer spacewalks more plausible and pleasant.
This week, scientists from Nankai University took a step towards smart clothing that rapidly adjusts body temperature using only solar power. The team fashioned a flexible material that captures sunlight to store and transfer heat. During the day, the patch removes heat from the skin and stores excess energy. At night, when it’s cooler, it releases this energy cache to heat the skin to comfortable levels.
Because the unit is powered by solar energy, it can maintain skin temperature without a battery pack. The patch can also rapidly adjust to ambient temperature swings by automatically switching between cooling and heating modes.
In a test, the team placed the patch on a volunteer’s hand and cooled their skin over nine percent in just seconds. The patch could keep the skin comfortable when exposed to a wide range of temperatures—from freezing to Death-Valley-level heat.
Rather than designing clothing made entirely from the material, the team envisions it can be strategically woven into everyday fashion or spacesuits—with larger patches in the torso and back areas, and smaller ones tailored to the shoulders, upper arms, and the fronts of thighs. Even without covering the entire body, the patches’ high efficiency at storing and transferring heat can keep wearers comfortable all day—as long as there are a few hours of sunshine.
The device “opens many possibilities” for “expanding human adaptation to harsh environments,” wrote Drs. Xingyi Huang and Peng Li at Shanghai Jiao Tong University, who weren’t involved in the study.
Sci-Fi Fashion
It’s hard to beat nestling under a heated blanket while watching snow fall outside. In contrast, running out into the frigid winter air to chase down a gift package is a total nightmare—especially while wearing pajamas and slippers.
Our bodies aren’t built for extreme temperatures. The biological processes that let us think, feel, breathe, and digest all depend on proteins that function best between a small range of ambient temperatures. Called the “thermal comfort zone,” it’s roughly between 71 and 82 degrees Fahrenheit (or 22 and 28 degrees Celsius). Temperatures outside this range make the body sweat or shiver to keep our internal temperature in check. But these biological mechanisms fail in extreme heat or cold, resulting in heat stroke, frostbite, or even death.
Clothing can extend the thermal comfort zone by regulating skin temperature either passively and actively. Passive options don’t need a power source. Some, like hand warmer packs, use chemical reactions to generate and release heat. Others dissipate heat into the surrounding environment to cool wearers down or reflect body heat back onto the skin to keep it warm. Puffy jackets, cooling neck gaiters, or sweat-wicking fabrics fall into this category.
Active materials use an external power source to rapidly change a material’s temperature on demand. But high energy consumption makes it hard to maintain temperature all day, especially when the wearer is on the move.
Solar-Thermal Wear
The new study leveled up active materials by using a natural energy source: the sun.
The bendy material is like an open-face sandwich. On top is a flexible solar panel that rapidly converts sunlight into electrical energy and a storage module to capture excess power. The bottom, skin-facing side is an electrocaloric device—a thin film that rapidly changes its properties when exposed to electricity. Given an electrical zap, this layer absorbs heat and lowers ambient temperature. Turning off the electrical field reverses the process and the device transfers heat to the skin.
The device can rapidly switch between heating and cooling cycles, and unlike previous rigid versions, the material is bendable and can contour to human skin like a Band-Aid.
In one test, the team placed the material on a volunteer’s hand and varied the ambient temperature between chilly and very toasty. They monitored the volunteer’s skin temperature with an infrared camera.
The small patch attained comfortable temperatures within seconds of ambient temperature changes. It was also self-sufficient, easily operating for a full day on twelve hours of sunlight.
Into the Unknown?
The new system broadens our skin’s natural thermal comfort zone. The “impressive” expansion makes it possible for the body to “adapt to more complex and changing environments,” wrote Huang and Li.
One potential application is weaving the material “into a conventional spacesuit to help reduce the overall power requirements,” wrote the team. Though finding space (no pun intended) could pose a challenge. A fitted spacesuit has only so much area exposed to sunlight, which limits the size of the panels. Roughly 60 percent of a spacesuit will have to be covered by the material to power it for a full day without an external battery source.
Also, even on Earth, dwindling sunlight in winter makes it more difficult to charge the material—especially if exploring polar regions where daytime all but disappears.
The team is already working to make the material more practical. One idea is to use temperature-sensitive electrical components that could further boost the patch’s temperature control range. Another is to add chemicals that increase the patch’s ability to conduct electricity, making it more efficient at storing and transferring heat. Linking multiple electrocaloric layers head-to-toe could also increase the device’s ability to handle temperature changes.
To Huang and Li, the material has far more uses beyond clothing. It could coat vehicles or buildings to keep temperatures in check without air conditioning. With extreme temperatures taking more lives than hurricanes, floods, or tornadoes combined, these materials aren’t just for intrepid explorers—they could change our everyday lives.
Image Credit: Kajetan Sumila / Unsplash
