Has a large percentage of voids and is lightweight, so therefore has the ability to float in water.

The answer is - Sponge.
Sponges are very lightweight, they have large percentage of voids as well, this practically means that they have low density structure. Their density is smaller than the density of the water, so this means that it will float on the water instead of sinking. 

Pumice stone has a large percentage of voids and is lightweight, so therefore, has the ability to float in water.

Explanation:

Pumice is one unique type of volcanic rock which resembles a sponge that is artificially made. It is made up of volcanic glass and contains a number of voids which act like small packets of air allowing the stone to float on water. Its composition makes it light in weight and also mostly light in color.