Here's why:

* Particle Size: Sand particles are the largest among the common soil types (sand, silt, clay). This means there are larger spaces between the particles, creating larger pores.

* Porosity: The larger the pores, the higher the porosity (the amount of empty space in the soil).

* Permeability: Permeability is the ability of water to flow through the soil. Larger pores allow water to move more easily and quickly, resulting in higher permeability.

Important Note: While sand has the highest permeability, other factors like compaction and the presence of organic matter can influence a soil's permeability.