How a Squid’s Color-Changing Skin Inspired a New Material That Can Trap or Release Heat
The stretchy ‘thermocomfort material’ has potential energy-saving applications in buildings and wearables
In the video that set materials scientist and chemical engineer Alon Gorodetsky on the path to his latest invention, an octopus appears from the algae like a jump scare in a horror movie. The creature shifts out of its camouflage coloration so rapidly it seems to materialize out of the seawater. That “remarkable” video, says the associate professor at University of California, Irvine, “really changed the trajectory of my career, because I started working on materials inspired by cephalopods.” Most recently, Gorodetsky took inspiration from a squid—specifically its color-changing skin—to create a new material that can keep in or let out an adjustable amount of heat. “Thermocomfort material,” as his team describes in the journal Nature Communications, has an array of potential uses, from heat-regulating clothing to energy-saving coatings for rooftops.
Squid have organs called chromatophores that can rapidly expand and contract, going from pinpoints to spots of color 14 times wider in less than a second. The changing dimensions of their spots mean that different wavelengths of light can be reflected from a given point on the animal’s skin depending on whether the squid’s muscles have shrunk or enlarged the chromatophores. Instead of looking at visible light waves, Gorodetsky and his team were interested in reflecting infrared light, which we feel as heat. The researchers have made a material that consists of a thin film of copper—which very effectively reflects infrared heat—on top of a stretchy, substantially-less-reflective layer of rubber. The copper layer is covered with hairline fissures, so when the thermocomfort material is tugged at, the reflective copper pieces pull apart, allowing heat to escape through the polymer (rubber) between them.
Gorodetsky has a handy analogy to explain his lab’s invention: “Imagine you’ve got a frozen lake or a frozen ocean, and it’s covered with ice floes, all these chunks of ice that are all bunched up next to each other. That’s what the material basically looks like in its inactive and un-stretched state. When you stretch it, you spread all the ice floes apart, so in our case, you can see the polymer underneath them.” When heat hits the polymer in between the copper “floes,” it is transmitted through the material instead of being reflected back towards its source. Due to the copper layer, the material—an “extremely light, stretchy rubber,” in Gorodetsky’s words—is shiny, although its color lightens as it stretches.
At its warmest, the thermocomfort material traps (or reflects back towards the body) heat almost as effectively as a space blanket, that crinkly aluminum foil-looking material that’s been used to reflect the sun’s glare in space and maintain marathoners’ body warmth after races. A sleeve made from thermocomfort material increased the temperature of the wearer’s forearm by nearly one degree Celsius, close to the heating power of a space blanket. But the thermoregulating material is also impressively versatile. At different degrees of stretching, it can make wearers comfortable across an 8.2-degree Celsius (roughly 15-degree Fahrenheit) span. When it’s 30 percent stretched out, it resembles the insulating ability of a Columbia Omni-Heat fleece; at 50 percent stretch factor, the material keeps heat in like wool. When researchers stretched thermocomfort material to double its original length, heat passed through it as if it were cotton. And even after researchers expanded and contracted the material 1,000 times, the repeated use didn’t wear it down.
Because the thermocomfort material was tested with the copper as the inner layer touching the wearer’s skin, this meant it kept the user warm when in its compact state, by keeping their body heat in. But if you flipped the material, Gorodetsky says, it would keep heat out, like a shiny sun shade placed on a car windshield.
In the Nature Communications paper, the engineers posit a variety of applications, among them the possibility that thermocomfort material could play a role in reducing the amount of energy dedicated to keeping spaces temperate, which accounts for a third of the energy consumption of commercial and residential buildings worldwide. Manufacturing the material should, Gorodetsky says, be as inexpensive as mass-producing space blankets, which cost under $4 at REI, and stretching it takes minimal energy, compared to the energy costs of a heat pump or air conditioning system. He imagines the coppery material coating rooftops and windows, or layered on tents or other outdoor equipment to control heat flow. It could be used, he speculates, to help dissipate heat from electronics (think, for example, of how quickly a laptop can get uncomfortably warm). Gorodetsky also mentions smaller, everyday applications, like Tupperware-esque containers to keep perishable food cold.
Gorodetsky says his lab is most excited about the impact the material could have on clothing. “If you had a jacket that everyone could wear, and every single person could adjust to keep themselves comfortable over a broader temperature range, then you just need to put in far less energy to keep the building at one single temperature,” he explains.
The team has applied for a patent, although figuring out how to mass-produce thermocomfort material is the next step before it can find commercial applications. “Translating this specific [innovation in materials science] directly to clothing takes a fair amount more engineering,” says Lucy Dunne, co-director of University of Minnesota’s Wearable Technology Lab, who was not involved in the research. “The biggest question mark for me,” Dunne says, is, “How do you get it to stretch?” Dunne floated several options, from low-tech straps that adjust the tightness of a garment to the more futuristic-sounding idea of integrating it with materials that are trained to shift shape based on thermal triggers. Another engineering challenge, Dunne says, will be ensuring thermocomfort cloth is breathable enough to meet consumers’ expectations of comfort.
Dunne sees the material as potentially useful in military camouflage equipment, helping hide soldiers from infrared sensors. Interest in thermo-regulating wearable technology seems to be on the rise, she says. Current approaches include devices, like the Embr Wave, which serves as a “personal thermostat” wristband that runs an electric current through ceramic or metal plates, or her own research incorporating conductive thread into electric-powered fingerless cuffs that distribute heat across the wearer’s hand. Infrared-reflective materials like space blankets or Columbia’s Omni-Heat exist, but the built-in insulating adjustability of Gorodetsky’s thermocomfort material sets it apart.
Next time you find yourself chilly and grabbing your “office sweater,” just think: maybe one day you’ll be wearing a coppery jacket, and all it will take to make yourself comfortable is a touch of a button or a tug on the sleeve.