Hm....I have a white Ferret that has nice translucent, hollow-looking fibers. Could be similar to the wing shown, if the ends are clipped. Or...this could be an animal that was previously sheared, so the ends wouldn't be naturally tapered. Llama? Alpaca?
Too thick for sheep, methinks, or cat. Also seems too thick for any canine or rabbit. Seal? Maybe. Polar Bear is possible. Goat? Antelope? Beard from the Amish?

If it is a synthetic...looks like dental floss but not thick enough for that. I'm coming up empty on synthetic ideas that we haven't covered already. UNCLE UNCLE!