Clayey soil has the least porosity because clay particles are extremely fine (<0.002 mm) and pack tightly together, leaving minimal air space. Despite having high water-holding capacity, clay has very low macro-porosity (large air-filled pores) and extremely low hydraulic conductivity, making it poorly drained and compacted. Loamy soil (optimal mix of sand, silt, clay) has good porosity; peaty soil (organic matter) has high porosity and water retention; silty soil has intermediate porosity.