Source : Webster's Revised Unabridged Dictionary (1913)

Perviousness \Per"vi*ous*ness\, n.
   The quality or state of being pervious; as, the perviousness
   of glass. --Boyle.

Source : WordNet®

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