Hi All
Just to chuck some 'oil' on the water. I asked the same question to Marc Petitjean over dinner this spring. His company prepares loads of the stuff for the fly tying market. He said that at first washing the feather loses about 20% of its natural oil..........in dying it loses about another 10%. So 30% gone from the natural if its washed and dyed. Marc recomends that some CDC oil is added to enhance the floating quality of the dyed feather.
In essence, stick to the natural if you want it to float without fiddling with it.
I disagree with the arguement that the fibrils are what keep the fly afloat.
Cheers
George Barron