If I had to guess, I'd say that a smooth surface is better than a rough one for cutting wind resistance. And I'd be wrong. There's a reason golf balls have dimples: The dimples decrease the drag caused by wind, by a significant amount. In the middle ages Dutch men used to hit spherical pebbles with a stick to play what became golf. Later in the 1600s they started using wooden balls. And it was in the late 1800s when players noticed that that beaten up balls went further than the smoother, newer versions.
Now researchers have created a material that—when triggered by wind—can automatically morph into a dimpled surface similar to that of a golf ball. It sort of also resembles pruning of finger tips after soaking in water (in fact, the inspiration for this new material came from dried prunes.) See the video below from the MIT team led by Pedro Reis, who developed the "Smorph" (Smart Morphable Surface).
The Smorph operates on fairly basic mechanics. In fact, the useful function comes from a common mechanical failure that most engineers need to prevent at all costs: Buckling. The prototype is a hollow silicon ball covered in a thin and stiff layer of polystyrene. When the pressure lowers within the hollow ball the exterior automatically shrinks, and this creates the dimples. The key thing is to have a pattern of dimples—and not something random.
Apparently the 'smart' part of the equation is that the depth of dimples can be accurately controlled by the pressure within the ball—and this is controlled by external wind conditions, otherwise called "complex surface topography on demand." Apparently the team was able to show that the material can reduce drag by an incredible factor of two. This is really significant.
Even though the prototype is spherical the team says the material should be able to come in many shapes—and so be used to decrease the drag experienced by airplanes or cars.
This isn't so far-fetched since, in 2009, the prescient crew over at Myth Busters already tried to literally coat a car with a golf ball-like texture to see if it reduced drag. Amazing.