Feathers are very light structures. They are composed primarily of keratin, the same material which makes up your fingernails. The hollow central shaft contains many small projections called barbs. Barbules are smaller structures attatched to each barb, and barbicels are found on each barbule and are smaller still. The barbicels are shaped like hooks and latch on to one another firmly, creating a strong, stiff hold that catches the wind and is literally "as light as a feather". Often part of a bird's incessant cleaning routine is the straightening of wing primaries, which seems to help reattatch the barbicels so the wings remain fully functional.
In bedding, plumage from a goose or duck. Though also lightweight, feathers are heavier than down, with quills that give them a resilient spring.
Light, hollow-shafted growths forming the plumage of birds. Both springy and soft, feathers appear alongside down on ducks and geese.