In the science professions and fields, the words permeable and impermeable are often used to describe whether or not a material or substance can allow liquids or gases to pass through its surface.

Permeable surfaces contain pores or openings that allow liquids and gases to pass through. These surfaces can be penetrated. Some common permeable surfaces are gravel, porous materials and grass.

Impermeable surfaces do not permit the passage on any liquids or gases. These surfaces cannot be penetrated. Some common impermeable surfaces include concrete, asphalt and concrete/clay paving blocks.

The underlying difference between permeable and impermeable surfaces and materials is the ability to allow the passage of liquids and gases. Due to the nonporous nature of impermeable surfaces, they cannot permit liquid and gas to enter and pass through like permeable surfaces and materials can.