Permeables

Permeables is a term sometimes used to refer to materials that permit the passage of fluids or gases. In geology, civil engineering, and materials science, permeability is the primary property describing how easily a fluid can move through a medium when driven by a pressure difference.

The permeability of a material is controlled by the size, shape, and connectedness of its pores or fractures, as well as saturation, temperature, and fluid viscosity. Porosity provides the fraction of void space, but connectivity and tortuosity determine whether those voids form continuous pathways. Therefore, high porosity does not guarantee high permeability.

Permeability is measured using tests such as Darcy's law-based methods: constant-head or falling-head tests for liquids; gas permeability tests for gases. The unit darcy is commonly used, with 1 darcy roughly equal to 9.87×10^-12 m^2 in SI units; in practice, hydraulic conductivity is a related measurable quantity.

Examples of permeables include sandstone, fractured rock, gravelly soils, textiles, membranes, and permeable pavements used to infiltrate surface water.

Applications of permeable materials span groundwater management, oil and gas reservoir engineering, filtration and membranes, civil construction, and environmental remediation. In everyday language, permeable materials contrast with impermeable materials such as clays or tight rocks.