Unlike the hairs of humans or other mammals, polar bear hairs are hollow. Zoomed in under a microscope, each one has a long, cylindrical core punched straight through its center. The shapes and spacing of these cavities have long been known to be responsible for their distinctive white coats. But they also are the source of remarkable heat-holding capacity, water resistance, and stretchiness, all desirable properties to imitate in a thermal insulator.

"The hollow centers limit the movement of heat and also make the individual hairs lightweight, which is one of the most outstanding advantages in materials science,” said Assoc. Prof. LIU Jianwei from USTC. To emulate this structure and scale it to a practical size, the research team-additionally co-led by Prof. YONG Ni from USTC-manufactured millions of hollowed-out carbon tubes, with each equivalent to a single strand of hair, and wound them into a spaghetti-like aerogel block.

Compared to other aerogels and insulation components, the researchers found that the polar-bear-inspired hollow-tube design was lighter in weight and more resistant to heat flow. It was also hardly affected by water-a handy feature both for keeping polar bears warm while swimming and for maintaining insulation performance in humid conditions. As a bonus, the new material was extraordinarily stretchy, even more so than the hairs themselves, further boosting its engineering applicability.

Scaling up the manufacturing process to build insulators on the meter scale rather than the centimeter one will be the next challenge for the researchers as they aim for relevant industrial uses. “While our carbon-tube material cannot easily be mass produced at the moment, we expect to overcome these size limitations as we work toward extreme aerospace applications,” said Prof. YU.

This image shows electron microscopy of the hollow bioinspired carbon tube aerogel. (Image by ZHAN Huijuan)