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Ducks are famously water-repellent. We even have a figure of speech that  recalls their ability to stay dry -- “like water off a duck’s back.” But that’s not actually the full picture.

See, ducks don’t so much stay  dry, as get wet with style. And the physics that let them dry off  quickly, and keep from getting waterlogged, have only recently been uncovered. This has been a mystery!

So duck feathers are hydrophobic,  meaning they repel water really well. Ducks normally secrete oils  to coat their feathers in, but even without those oils, the  structure of the feathers keeps water out. The feathers have a rough texture  with tiny gaps in-between the branching structures of the feather.

Those pores trap teensy air  pockets within the feather, helping the ducks keep warm and  reducing drag when they dive. But something happens to those  air pockets as the ducks dive. As they go deeper and deeper, the  surrounding pressure increases, and that forces water into the duck’s feathers.

And if the water reaches all the way to  their skin, the duck gets waterlogged and loses all the nice insulation and  reduced drag from that trapped air. But ducks have a trick up their feathered  sleeves: they have multiple feather layers. And scientists have finally figured  out how that works to keep water out.

In a 2021 study, researchers stacked  duck feathers on top of each other inside a pressure chamber. Then they added a little pool of  water on top of the stack, and slowly cranked up the pressure  while a camera captured the results. And the more layers there were,  the more pressure was needed to push water through to the bottom layer.

Because when water gets  squeezed through the pores, it’ll go through the easiest route. But the more layers you  have, the less likely those easy-to-get-through pores are to line up. Think about it kind of like trying  to get through a hedge maze.

Adding more layers basically  adds a bunch of dead ends, and the water ends up trapped. The researchers also made their  own, synthetic feathers out of aluminum foil with tiny slots  cut out with a laser cutter. That would let them confirm that what  they were seeing was to do with the structure of the feathers,  not something else like the particular duck feathers they happened to have.

And the synthetic feathers  showed a similar effect. The really cool part is that it looks  like ducks may have adapted to have just the right number of feather  layers to make sure there’s always an air pocket there. Ducks that dive deeper have  more feather layers to withstand the greater pressure at those depths.

At least, that was the case for the  three species of duck in this study. And the scientists who did the work  said this lasagna-like layering probably exists in most waterfowl. The researchers also say their fake duck feathers could have some real applications.

You could put something like those  aluminum feathers on the outside of boats to reduce drag, or stop barnacles from sticking. But it doesn’t need to be practical for  it to be pretty cool that there is some very neat physics hiding  out in something so mundane.

Ducks: get wet with style. If you want to learn even  more physics of the everyday, you might like Brilliant’s  course… Physics of the Everyday. You’ll learn about the secrets  behind not just ducks, but refrigerators, water towers, and more. Brilliant’s courses have always been  interactive, but now they’re getting an upgrade, with brand-new formats for  courses like pre-algebra and mathematical fundamentals to keep you even more engaged.

That means you’ll learn even more  from their host of courses in science, math, engineering, and computer science. If you’re interested, you can sign up  at brilliant.org/scishow to get 20% off an annual Premium subscription.  So thanks for your support!