Clay has the smallest particle size of any soil type, with individual particles being so small that they can only beviewed by an electron microscope due to that, they have slow permeability resulting in a very large water-holdingcapacity. Because the soil particles are small and close together, it takes water much longer to move throughclay soil than it does with other soil types. Clay particles then absorb this water, expanding as they do so andfurther slowing the flow of water through the soil.