One of the guys who learned how to tie the wool/satin jigs from the guy who came up with them says this.
the "batting" is the white fluffy, easy to pull apart, material that is under sheets in bedding. A nice little girl at JoAnn's Fabrics explained this to me, as she directed me to huge rolls of the stuff. When I researched it, "batting" can be composed of cotton,polyester, and/or wool ;singly or in a blend,each material holds water very well.Tying is easy with batting -ya just pull out a chunk,stretch it to a longish shape, then tie its middle to the neck of the jig and fluff each half to extend beyond the hook bend. Easy to tie satin on either side or around the batting base for that robust look.
So any fabric stores should have it.