It's not the easiest stuff to tie with - a fairly precise mix of guard hair and underfur is require to achieve the correct balance of floatability without creating excessive bulk and a lot of people abandon the pattern after getting this wrong and finding it doesn't fish properly.
Perseverance will definitely be rewarded though - the pattern below is one of the best I've ever used for tricky fish feeding on olive duns. When the hatch begins to tail off and the fish become picky and your usual patterns begin to get refused, then this one will redress the balance good and proper:
Trust me, it's a good 'un!
Happy Christmas,
Matt