Feathers help chickens stay warm by providing insulation. The structure of feathers traps air, which helps to keep the chicken’s body heat from escaping. Chickens have a layer of down feathers close to their skin that helps to keep them warm, and they also have contour feathers on the outer layers of their body that provide additional insulation.
Chickens also fluff up their feathers when it is cold to create additional air pockets and increase the insulating properties of their feathers. In this way, feathers help chickens to maintain a stable body temperature even in cold weather.
TBN Ranch Chicken Keeping Resources 