Feathers streamline the bird's body to make it more aerodynamic, provide lift and thrust for flight, and create insulation to help maintain high body temperatures. Varying in shape, structure, and purpose, five major feather types include contour, semiplume, down, filoplume, and bristle. Contour feathers are the most obvious as they make up most of the feathers that are generally seen, such as the outside feathers on the body and wing and tail feathers. The base part of the shaft is called a calamus, while the portion within the vane is called the rachis. The vane consists of interlocking barbs that grow on either side of the rachis.
Close examination reveals additional structures growing out from the barbs called barbules.
Barbules on the side of barbs closest to the bird are called proximal, while barbules on the side of barbs away from the bird are called distal. Proximal barbules of one barb overlap with distal barbules of another barb. Proximal barbules are generally smooth with rolled edges, while distal barbules possess tiny hooks. When the hooks of the distal barbules overlap and attach on the edges of the proximal barbules, the two barbs are connected. This creates a vane that is both rigid and flexible.