impermeability

Impermeability is the property of resisting the passage of fluids or gases through a material or boundary. It describes the degree to which a substance or barrier prevents permeation by liquids, vapors, or gases. It is the opposite of permeability.

In geology, impermeable layers such as dense rock or clay caprock hinder groundwater movement and are essential in constructing wells and containment systems. In civil engineering and construction, impermeable barriers resist water ingress and are used in waterproof membranes, foundations, roofing, and infrastructure to protect indoor spaces and prevent contamination.

In materials science, impermeability is quantified by permeation rate or permeability coefficient. For gas permeability, units include Barrer; for water vapor, g/m2/day. Measurements involve standardized tests such as diffusion tests or gas permeability tests. The concept is broader than absolute blockage; high impermeability means very low permeance.

In biology, membranes are often described as selectively permeable rather than impermeable, allowing certain substances to pass while blocking others. They may utilize channels, pumps, or other mechanisms to regulate passage.

Limitations: no material is perfectly impermeable under all conditions; temperature, pressure, and chemical environment can alter permeability. Achieving impermeability involves material selection, barrier layers, and sealing techniques.