Lay a thread base and tie in the tail barbs at the bend.
Tie in the brown ribbing thread, then dub a slim body of mayfly yellow kapok forward to the 65% mark. Kapok is roughly eight times lighter than cotton and extremely fine, so it builds a floating body without bulk. You can take this dressing down to very small hooks and still keep a slender profile.
Rib forward with the brown thread in evenly spaced open turns for segmentation.
Tie in natural grey CDC as the wing over the thorax.
Whip finish. The kapok body floats the fly on its own; keep floatant off the CDC.