- Calamus: The hollow barbless central base stem of the feather.
- Rachis: The central spine of the feather that branches into barbs.
- Barbs: The barbs have the "feathery" barbules.
- Barbule: The barbules have small hooks that interlock with nearby barbules.
Fluffy feathers such as those used in down feather pillows look fluffy because they have a loosely arranged microstructure which is described as "plumulaceous". Plumulaceous feathers keep the bird's body warm. The flat, stiff feathers are called "pennaceous" feathers. The pennaceous feathers protect the bird from water and the elements, and allow the bird to fly.
The shapes and colors of bird feathers are very diverse which helps protect the birds and give visual communication cues to one another to warn of predators and for mating.