undurchlässige

Undurchlässige is the feminine singular or plural form of the German adjective undurchlässig, meaning impermeable or not permeable. It describes materials, barriers or membranes that do not allow passage of liquids, gases or other substances. The term is used across technical and everyday language to distinguish between barriers that block transmission and those that permit it (durchlässig).

In geology and hydrology, undurchlässige Schichten or Gesteine block groundwater movement and can form aquicludes or aquitards when contrasted with permeable layers. In civil engineering and construction, undurchlässige or waterproof components—such as seals, membranes and coatings—aim to prevent water ingress and leaks. In textiles and fabric technology, undurchlässige fabrics protect against water or wind, though many such materials may still be breathable to some extent when designed with air-permeable membranes.

In biology, the concept appears in reference to membranes or barriers, though many biological membranes are semipermeable rather than completely undurchlässig. The term thus often conveys a clear contrast to durchlässig, which denotes permeability, and to related nouns like Durchlässigkeit (permeability) and Wasserdichtheit (water tightness).

grammatically, undurchlässig is the base adjective; its form undurchlässige is used attributively with feminine singular nouns (die undurchlässige Wand) and with plural nouns (die undurchlässigen Materialien) in standard German. The prefix un- systematically marks the negation of permeability, yielding the common concept of a barrier that resists passage.

Overall, undurchlässige describes the property of being impervious to transmission, applied in contexts ranging from geology and engineering to textiles and biology.