impenetrability vs imperviousness

impenetrability and imperviousness both are nouns.

Word	Noun	Adjective	Verb	Adverb
impenetrability	Yes	No	No	No
imperviousness	Yes	No	No	No

As nouns, impenetrability and imperviousness are synonyms defined as:

impenetrability and imperviousness: the quality of being impenetrable (by people or light or missiles etc.)

impenetrability (noun)	imperviousness (noun)
the quality of being impenetrable (by people or light or missiles etc.)	the quality of being impenetrable (by people or light or missiles etc.)
incomprehensibility by virtue of being too dense to understand