Density. So the basic answer is that sweet potatoes are less dense than regular potatoes, (and water) causing them to float rather than sink.

Should potatoes float or sink?

Potatoes sink in regular water, but they'll float in salt water or sugar water.

What does it mean if a potato floats in water?

Explanation: If the potato floats or not have to do with its and the water's density. The potato has a higher density than the water and therefore it sinks to the bottom. When the salt is mixed in the water, it gets more density than the potato, and the potato floats.