There's down and then there's down - and feathers are not down. But the feds permit a certain amount of feathers in products labelled "down" because of the difficulty of separating down from feathers. New technology has replaced hand separation so now we can have much higher-volume down than in the past - as well as fewer feathers. Unfortunately, the feds have gone to a volume testing procedure that inflates the volume. The old measure approximated performance under field conditions, the new one does not. So, 900 cu.in. is the new 800. And it is better to call it 750 for calculating how much to order to fill whatever shell you have made.
Here's one source for information on down. http://www.competitionbureau.gc.ca/epic/site/cb-bc.nsf/en/01237e.html#III
"Down" is the undercoating of waterfowl (goose, duck or swan) and consists of light, fluffy filaments growing from a central quill point, thereby creating a three dimensional structure which traps air and gives down insulating ability. The properties of down which make it so popular are its light weight, compressibility, recovery power, resilience and breathability.
"Feathers" are the individual horny structures which form the outer body covering of birds and consist of a quill point, quill shaft, vanes and usually an aftershaft. Feathers share the same properties as down, however, since they are two-dimensional structures, they do not trap air as efficiently and are, therefore, generally not as good insulators. As a rule, waterfowl feathers are superior to landfowl feathers with respect to both filling power and resilience.
This site also explains what claims are permissible under current regulations.
Note that it is the feathers that are coming out. Just about any fabric is down-proof, but only tightly woven fabric will resist the needle-like quills of feathers.
Makers used to debate the virtue of feathers in a fill mix. The idea was that since feathers had stiff quills, they would help loft heavy shells. That is spurious, IMHO because down itself is extremely elastic and will do the job without any help. It is so elastic that it was once used as the core of golf balls. Dig it! Feathers are just extra weight that does little except reduce the compressibility of a garment and poke holes in the shell.