The biggest difference lies in the place where you find them on the goose. Feathers are located on the wings and the outer layer of the body. They help to protect the animal against cold and wetness, making them heavier and more rigid. The hard quill can, especially when there are many feathers in the filling, also cause a prickly feeling. But those quills can also break, meaning the filling will need replacement after a while.
Down, on the other hand, is located between the feathers on the goose's belly and doesn’t have a quill to attach itself to the body. This results in a lighter material, which also insulates well. Because only in this way can a goose maintain its own body temperature in cold areas.