Diamond
His shield was made of an impenetrable material.
None. No material is indestructible.
Impenetrable- The fort's defenses were thought to be impenetrable.
His skin was impenetrable, Impenetrable means difficult to get through such as a forest or your skin. the forest was impenetrable and it took me hours to get through.
The man had impenetrable metal skin, incapable of being pierced.
Bwindi Impenetrable National Park was created in 1991.
Impenetrable is more of an Adjective, it's used to describe a trait, or as in Impenetrable, it's describing how something cannot be penetrated. Penetrate itself would be a verb.
The area of Bwindi Impenetrable National Park is 331 square kilometers.
The professor's heavy accent made the substance of his lecture nearly impenetrable.
The steel curtain
Opaque.
The phrase "wrapped in an impenetrable mist" could mean that the area is covered in thick fog that you can't see through. If it is being used symbolically, it could mean that an area is undiscovered, or even that someone is unable to think straight (as in "my mind was wrapped in an impenetrable mist").