Source : Webster's Revised Unabridged Dictionary (1913)

Penetrability \Pen`e*tra*bil"i*ty\, n. [Cf. F.
   p['e]n['e]trabilit['e].]
   The quality of being penetrable; susceptibility of being
   penetrated, entered, or pierced. --Cheyne.

Source : WordNet®

penetrability
     n : the permeability of something that can be penetrated by a
         liquid [syn: {perviousness}] [ant: {impenetrability}, {impenetrability}]