Down comes from the plumage of a bird, usually waterfowls. The plumage is the soft, fluffy undercoat that lies beneath the tougher feathers at the underbelly. The most common types of down come from ducks and geese. In either case, the more mature the bird is, the larger its plumage tends to be. This results in a greater loft and a higher down fill power rating.
Down gets formed into clusters which are then used for items such as jackets, pillows, comforters, sleeping bags, and other such things. Each cluster is made of thousands of tiny fibers crisscrossing in every direction and the air pockets between them. Just like a sponge traps water, these down clusters trap your body heat while allowing the material itself to breathe. Down fill also has a phenomenal “warmth to weight” ratio.
As down is warm, lightweight, and breathable, it makes for an ideal insulator for outerwear. Many consider it to be the best insulator known to man.
For more information on the science behind down, please read our blog post at: https://triplefatgoose.com/blogs/down-time/down-is-the-natural-insulator-science-cant-make-better