They are light weight, strong, and can be made waterproof. Many can be repaired by stroking them from the base up, hooking them back together. Down feathers lack hooks so they will fluff out for insulation. Duck flight feather magnified at same rate as 1 cm ruler. Dark line through center is feather's shaft.
Barbs branch off from the shaft.
Duck feather at greater magnification with 1 mm for scale. Barbs show up here with their smaller branches, called barbules. Higher magnification with 1 ruler line for scale. Small hooks, called barbicels, can be seen on feather's barbules. Feathers can provide insulation, a water resistant body covering, ridgid surfaces for flight, even the sense of touch, all with minimum weight.