impenetrability vs impenetrableness

impenetrability and impenetrableness both are nouns.

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

As nouns, impenetrability and impenetrableness are synonyms defined as:

impenetrability and impenetrableness: incomprehensibility by virtue of being too dense to understand

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