surface that does not allow for infiltration and/or penetration of liquids.

Merriam-Webster Online Dictionary
impervious (adjective)
a) not allowing entrance or passage - impenetrable a coat impervious to rain
b) not capable of being damaged or harmed - a carpet impervious to rough treatment
not capable of being affected or disturbed - impervious to criticism
impervious (Wikipedia)

Permeability in fluid mechanics and the earth sciences (commonly symbolized as k) is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it.

The permeability of a medium is related to the porosity, but also to the shapes of the pores in the medium and their level of connectedness.

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