Aerogel is a synthetic gel whose liquid is replaced with gas. Although the gel—effectively a material—is still solid, its gaseous composition makes it extremely porous, much like an ultralight foam. Indeed, aerogel’s thermal conductivity is so low that it’s often touted as an ideal insulator. Although aerogel must be kept dry—its structure deteriorates when wet—coated panels of the material have found their way into buildings for decades.
Unfortunately, aerogel is also fragile and difficult to process, problems that have hindered its application as a knittable textile. Over the past decade, researchers have made fibers out of aerogel using graphene, carbon nanotubes, cellulose, and other ingredients to improve their mechanical properties. Yet existing aerogel fibers remain too weak and inflexible to knit into practical clothing.
Led by material scientists Weiwei Gao and Hao Bai (both with Zhejiang University in Hangzhou, China), Mingrui Wu and colleagues have overcome both problems. Inspired by the structure of polar bear fur, they developed a method for creating aerogel fibers that are strong enough to be twisted or tied into woven configurations. They first fabricated a microscopic spool of aerogel thread, or core, using a technique known as freeze-spinning and then freeze-dried the result to retain its porous structure. Next, they encapsulated the core in a dense thermoplastic shell made of polyurethane. The combination—a porous inner core and dense outer shell, as shown above—prevents heat loss and makes the fibers waterproof and mechanically strong.
More than 90% air, the fiber’s core is extremely stretchable—up to 1000% strain. That’s nearly three orders of magnitude more than the 2% strain that traditional aerogel fibers can endure. And when coated with an 80-µm-thick encapsulating layer, each individual fiber is able to lift a 500 g weight without breaking.
As a proof of concept, Wu and colleagues wove a sweater, pictured here, made from the new aerogel fibers. Having just one-fifth the thickness of a down coat, the sweater provided comparable thermal insulation—even after 10 000 stretch-and-release cycles. The researchers’ measurements of the fabric’s thermal conductivity were lower than those of other common materials, such as nylon, polyester, and wool.
The researchers see promise for newly developed textiles as protective clothing—as military uniforms and protective suits to wear in extremely cold environments, for instance—and have demonstrated their durability. How quickly they or others can adapt the synthesis procedure for large-scale or commercial manufacture is unclear, however. They have already filed a patent for the process by which they make the fibers. But the rate at which aerogel can be spun into fiber is much slower than the rate at which more traditional materials can be spun. (M. Wu et al., Science 382, 1379, 2023.)
