Short answers, pulled from the story.
A down feather has a short or absent central shaft and barbules that lack the hooks found on contour feathers, giving it a loose, fluffy structure. This lack of interlocking structure allows the barbs to trap air, making down a highly effective thermal insulator. It is considered the most structurally simple of all feather types.
The three types are natal down, body down, and powder down. Natal down covers young birds during early development; body down lies beneath the outer contour feathers of adult birds; powder down is a specialized type whose barbule tips disintegrate into fine keratin particles. Powder down is found in parrots, herons, and tinamous, and the dust it produces is a known human allergen.
Eiderdown is collected from managed nests in Iceland, Scandinavia, and Siberia without harming the birds. Collectors take roughly 0.75 oz of high-quality down per nest halfway through incubation, then gather about another 0.75 oz after the ducklings leave, with 50-60 nests yielding roughly one kilogram total. Global wild-nest collection amounts to no more than four tonnes annually, with approximately 70 percent sourced from Iceland.
Fill power measures how many cubic inches one ounce of down displaces in a standardized cylinder test. Eiderdown holds the highest known fill power at 1200. Most outdoor equipment uses fill power in the 400-900 range, with down rated 500-650 suitable for most conditions and 800-900 used for very cold or ultralight gear.
In the Ghost Dance, a religious movement widespread among peoples of the Great Plains and Canadian Prairies, each dancer holds a painted feather tipped with a down feather painted a second color. The feathers are typically those of a crow, sacred to the Ghost Dance, or an eagle. Zuni prayer sticks incorporate eagle down, and the Hopi rub eagle down feathers over rattlesnakes during Snake Dances to calm them.
Live-plucking is illegal in Canada, the United States, and across Europe, but is documented as occurring in Poland, Hungary, and China. A 2009 Swedish documentary reported the practice might account for 50-80 percent of global down supply, a figure supported by IKEA and an industry representative but disputed by industry organizations. IKEA and Patagonia subsequently altered their product lines to exclude live-plucked down.