Cul De Canard (CDC) (French for "Duck bottom") is the fluffiest down feathers from the bottom of a duck; they are very buoyant and are used when tying dry flies. They owe their buoyancy to their proximity to the ducks preen gland which secretes an oil distributed by the duck as a cleaning and waterproofing measure. It is unnecessary for the angler to add additional oil by way of floatant. Flies incorporating CDC are easy to dress and popular with anglers and trout alike.
