I'd just buy regular yarn from the craft store, whatever color you want. With your 4 fingers together, wrap the yarn around them about 30 wraps (60 strands). Unstring the bow and separate the string bundles where you want the puff to be. Insert the wrapped bundle of yarn through the bow string and string the bow again. push the yarn bundle together tightly and trim each side 1 inch or so on each side of the bow string. The yarn will puff as you shoot. If it gets full of crap and burdocks, cut them off and re do it. Easy peasy, cheap too.