Incapable of being penetrated or pierced; not admitting the passage of other bodies; not to be entered; impervious; as, an impenetrable shield.

Not capable of being penetrated or entered (as a penguin's feathers are to water)

not admitting of penetration or passage into or through; "an impenetrable fortress"; "impenetrable rain forests"

Inaccessible, as to knowledge, reason, sympathy, etc.; unimpressible; not to be moved by arguments or motives; as, an impenetrable mind, or heart.

Term applied historically to the area of the dry chaco with the most inhospitable conditions for white settlement, due to lack of water; the name of a zone of northwestern Chaco Province.

permitting little if any light to pass through because of denseness of matter; "dense smoke"; "heavy fog"; "impenetrable gloom"

Having the property of preventing any other substance from occupying the same space at the same time.

Cannot get through.