CDC or Cul-De-Canard translates to duck butt. These are the softest feathers from the rump of a Duck. Also they have great qualities in the water. They really grab air bubbles giving the illusion of air bubbles on any given pattern making it look more life like.
CDC Puffs are great because of the fact they are smaller in size and softer than standard CDC. We use puffs on midges, emergers, and Compara duns. See Tying an RS2 with CDC Puffs
CDC- Standard feather size is great for larger midges such as chironomids and dry fly patterns. Longer fibers allows for a greater range of hook sizes.
Super Select CDC– These are the highest quality of feather, fullest plumage and allows the tier the greatest range of fly patterns.