It’s a polypropylene yarn, like EP Fibers (at 1/3 the cost), Widow’s Web, etc. Flytyer’s Dungeon sells it; they have a very nice color selection. I like it for wings on dries and emergers; seems to be hydrophobic, to a point. I dose it with floatant; after fishing it for a while a couple false casts shake out what water clings to it.
Regards,
Scott