Down vs. Feather: What's the Real Difference?

What's the difference between down and feather? 

Down and feather come from the same birds but serve very different purposes. Down consists of light, fluffy clusters found beneath the outer feathers—soft filaments that radiate from a central point without any quill. These clusters trap air to create exceptional warmth and a cloud-like feel. Feathers, by contrast, have a firm quill shaft with fibres extending from each side, providing structure and support.