impenetrableness vs impenetrability

impenetrableness and impenetrability both are nouns.

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

As nouns, impenetrableness and impenetrability are synonyms defined as:

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

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