Goose feather is silky at the base, with a slightly curved rachis and thick, well- developed filaments. Its only purpose is to be a protective shell against water and wind.

It is the down that keeps body temperature constant.

For this reason, while feather is suitable for the filling of cushions, down is perfect for clothing.

Down includes independent flocks, free from the central rod [rachis] that supports the feather. It is to be found under the wings, on the belly and on the neck of anatidae, and it is the noblest part of feathering. It weighs one tenth of a small feather. One gram of down includes about 350 to 600 flocks.

Its extremely thin filaments make it elastic and create air cells that maintain body temperature naturally.

Feather and Down Directory

"Down feather" by Wikipedia