Why don't ducks get wet?

Duck feathers are made of barbs and tiny hooked barbules that zip together, creating a surface so fine that water droplets sit on top instead of soaking through. Ducks preen constantly, spreading oil from the uropygial (preen) gland at the base of the tail, which helps keep the feathers in condition. Research suggests the feather structure itself is the main reason for water repellence, with the oil helping maintain it. Beneath the outer feathers lies a layer of fluffy down that traps air, keeping ducks warm and buoyant. That's where the phrase 'like water off a duck's back' comes from.