If you tie four size 18 Rusty Spinners, all with TMC 100 hooks, with identical microfibbet tails, identical poly yarn wings, identical Superfine dubbing thoraxes, same thread, but with four different abdomens made of:
2. Goose biot
4. Superfine dubbing
Which would float longer without any floatant being applied, again all things being equal? Or would the fact that they are such small flies on light hooks the abdomen material doesn't make any difference, as long as it is a material that doesn't immediately soak up water?