Thermal insulation design bioinspired by microstructure study of penguin feather and polar bear hair.

Nature is an amazing source of inspiration for the design of thermal insulation strategies, which are key for saving energy. In nature, thermal insulation structures, such as penguin feather and polar bear hair, are well developed; enabling the animals' survival in frigid waters. The detailed microscopy investigations conducted in this study, allowed us to perform microstructural analysis of these thermally insulating materials, including statistical measurements of keratin fiber and pore dimensions directly from high resolution Scanning Electron Microscope (SEM) images. The microscopy study revealed many similarities in both materials, and showed the importance of their hierarchically-organized porous structure. Finally, we propose the schematic configuration of a thermally-insulating structure, based on the penguin feather and polar bear hair. These optimized thermal-insulator systems indicate the road maps for future development, and new approaches in the design of material properties. STATEMENT OF SIGNIFICANCE: We present the first detailed comparison of microstructures of penguin feather and polar bear hair for designing optimum thermal insulation properties. This unique study involves the measurement of the sizes of pores and fibers of these two keratin-based materials, including the investigation of their 3D arrangements. We revealed porosity interconnection, especially in polar bear hair, which is one of the key designs exhibited by thermal insulation materials.