I have found the best "yarn" for flies like LaFontaine's Sparkle Pupa is a material I got from Ben Franklin called "Dazzleaire". It can also be bought on line or even through eBay.

When you get it, cut it in pieces about 1/4 to 1/2 inch long, and then put the cut pieces in a coffee blender and run it about 10 seconds and you will have a wonderful dubbing material!!!!