Adverb
In an impenetrable manner or state; imperviously.
Source: Webster's dictionaryEdward Kennedy “Duke” Ellington was the greatest jazz composer of the twentieth century—and an impenetrably enigmatic personality whom no one, not even his closest friends, claimed to understand. Source: Internet
Yang gazed out impenetrably from the shade of his newsboy cap. Source: Internet
At that time she seemed almost impenetrably cool. Source: Internet