Goose down
feathers in a jacket or bedspread
Fill power is rated by how an ounce of goose down occupies space. Average quality is about 500 and the amount increases with the quality of the down.
Why do you need to fill it up upside down? Why is it so much harder simply to fill it up right-side up? Gosh get a life and do things right. Stop trying to be all innovative and annoying...