Polar bear fur-inspired fibers offer exceptional thermal insulation, tested in a sweater

Inspired by the structure of polar bear fur, researchers present a knittable aerogel fiber with exceptional thermal and mechanical properties. The fibers are washable, dyeable, durable, and well-suited to be used in advanced textiles. This allowed the researchers to test them in a sweater that demonstrated impressive thermal insulation, among other features. Aerogels are an ideal material for thermal insulation. They demonstrate high porosity and extremely low thermal conductivity. However, the application of aerogels in insulating fibers for textiles has been limited because of their fragility and poor processability. Not only do they lack the strength and stretchability needed to weave or knit them into practical textiles, but current aerogel fibers are not machine washable and quickly lose their thermal insulation capability in wet or humid environments. Many animals that live in extremely cold environments have evolved specialized furs that keep them warm and dry. For example, polar bear hair is comprised of a porous core enclosed within a dense shell structure. As a result, the hairs provide outstanding thermal insulation while maintaining strength and flexibility. Mimicking the core-shell structure of polar bear hair, Mingrui Wu and colleagues used a freeze-spinning approach to create a strong polymeric aerogel fiber with lamellar pores. They then encapsulated it with a thin, stretchable rubber layer. The resulting encapsulated aerogel fiber (EAF) achieves excellent thermal insulation performance while also being mechanically robust, making it suitable for knitting or weaving. Despite the fiber’s high internal porosity (over 90%), Wu et al. show that the fiber is stretchable up to 1000% strain – a significant improvement compared to traditional aerogel fibers, which only achieve ~2% strain. The fiber maintained its thermal insulation properties with minimal impact even after 10,000 repeated stretching cycles at 100% strain. Moreover, the authors demonstrate that the EAF is washable and dyeable. As a proof-of-concept, Wu et al. wove a thin sweater made from the fibers, which, despite being roughly one-fifth as thick as a down jacket, provided comparable insulating performance. In a related Perspective, Zhizhi Sheng and Xuetong Zhang discuss the study in greater detail.