Humboldt penguin’s feathers are full of tiny, micrometer-scale interlocking barbs. This creates a dense net of fibers that water can’t penetrate—and it also traps air bubbles that prevent heat transfer, keeping water from freezing on the feather’s surface.

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Humboldt penguin’s feathers are full of tiny, micrometer-scale interlocking barbs. This creates a dense net of fibers that water can’t penetrate—and it also traps air bubbles that prevent heat transfer, keeping water from freezing on the feather’s surface.