barbules

Barbules are the tiny projections that extend from the barbs of a bird’s feather. A feather consists of a central shaft with barbs radiating from it; each barb bears numerous barbules along its length. Barbules are slender filaments that may carry minute hooklets on their distal ends.

In many feathers, especially flight feathers, barbules from adjacent barbules interlock with hooklets to form a continuous, cohesive vane. This interlocking reduces air turbulence and helps maintain a smooth surface that contributes to aerodynamic efficiency, waterproofing, and insulation by keeping the feather structure intact during movement.

Down feathers differ in their barbule structure. They have shorter barbules and often lack developed hooks, producing a fluffy, insulative layer that traps air rather than forming a rigid surface. The density, length, and hooklet presence of barbules vary among species and feather types, reflecting adaptations to flight, weather, and display.

Barbules grow as part of feather development and are shed with the feather during molt. Their microstructure has attracted interest in avian biology and biomimetics, as the lightweight, resilient interlocking system inspired surface technologies and material design.