A thin layer of air is trapped by the microsculptural bumps on ducks’ feathers making for a silvery sheen (called a plasteron) when feathers are dipped into water. It’s about surface tension. But if a bird dives deeper than several meters, the pressure of the water overcomes the surface tension, potentially soaking the feathers. But the feathers still remain dry! How? The ability to stay dry under the pressures of deeper water has to do how the birds’ preen oil changes the pressure needed to fully soak the feather. This allows deep divers’ feathers to just shed the water when the bird surfaces rather than getting soaked. *