DOWN is the soft, fine, under plumage of birds found beneath the tougher exterior feathers. Very young birds are covered only in down. Down is very resilient and a wonderful natural form of insulation as it has good lofting characteristics, trapping small pockets of air efficiently to provide a thermal barrier. This helps the birds to stay warm in the winter and cool in the summer. Feathers, on the other hand, repel water and keep the bird dry. Feathers also have a quill, whereas down is merely fluff and does not contain a quill.