Permeability refers to the ability of water to move through soil or other porous material. The more permeable a material is, the easier it is for water to flow through it. When water encounters a permeable material, it can infiltrate and flow through the tiny spaces between the particles that make up the material. If a material is not very permeable, on the other hand, it may resist the flow of water or even block it entirely. Factors that can affect permeability include the size and shape of particles in the material, the amount of pore space, and the presence of voids, fractures or channels that allow water to move through the material more easily. In general, materials that are more porous or have more pore space are more permeable and thus allow for faster and easier movement of water.