According to Patagonia, there are two reasons why the bar system works. One, the wide bars and strategic spacing covers more surface area than studs. And two, the aluminum is hard enough to cut through rock snot, but soft enough to grip the rock under the slime. If you look closely at the photo above, you can see the scrapes and pits on the aluminum from the metal "grabbing" the rocks. For reference, the boots were brand new when I put them on, and that photo was taken after one full day of wading.