Cross sections of polar bear hair and biomimetic fibre

The insulating structures of a polar-bear hair (left) and a fibre mimicking it (right) are clearly visible under a scanning electron microscope. Credit: Y. Cui et al./Adv. Mater.

Materials science

A thermal-invisibility cloak spun from silk and ice

Artificial fibre inspired by polar-bear hair confers superior insulation.

The thick pelt that helps polar bears to survive frigid Arctic winters has inspired a warm, sturdy fibre.

The core of a polar-bear hair consists of a sponge-like network of hollows, which help to make it a superb insulator. To imitate this structure, a team lead by Hao Bai of Zhejiang University in Hangzhou, China, devised a syringe that extrudes silk molecules mixed with water to form a fibre. The fibres are then chilled to create ice crystals between the silk particles. Next, the ice is driven off, leaving behind a core riddled with internal voids.

The researchers wove blankets from the material and wrapped them around rabbits. The blankets provided such efficient insulation that heat-sensing devices were unable to detect the rabbits’ warm bodies. Materials that confer such thermal invisibility could have both industrial and military applications.