Impact of Polar Bear Hair Microstructure and Young’s Modulus on Thermal Properties: A Luminescence Investigation

Polar bears (Ursus maritimus) have evolved exceptional thermal insulation for survival in the Arctic environment and studying their thermal regulation offers important insights into natural insulation mechanisms. This study examined the structural, mechanical, and optical properties of polar bear hair and compared them with brown bear (U. arctos) hair to understand their role in thermal regulation. Structurally, polar bear hair has a hollow core and contain “air pockets” that connect the hollow center (e.g., medulla) through the entire cortex. The diameter of these air pockets range from 1μm to 15μm. Mechanical testing showed the tensile strength of polar bear awn-down hair (1.6 ± 0.04 GPa) was lower than brown bear awn-down hair (3.6 ± 0.5 GPa), while brown bear guard hair is even stronger (4.8 ± 0.7 GPa). Optical analysis under UV (365nm) excitation showed that polar bear hair emits purple light, while brown bear hair shows no emission, highlighting distinct optical properties. Phosphor thermometry technique was used to map the response of both types of hair between −40 °C and room temperature. These findings advance our understanding of natural thermal insulation and inspire biomimetic thermal insulation designs.