Feather. Coloured scanning electron micrograph (SEM) of the structure of a feather. The flat broad vane of a feather is formed by comb-like rows of filaments called barbs, which project from either side of a central shaft (rachis, diagonally across centre). Each barb has rows of minute filaments called barbules. The barbules on one side bear hooks, while those on the other have a groove. This arrangement hooks adjacent barbs together, linking the whole structure. This makes the feather strong yet flexible and light, which is ideal for flight.