Source : Webster's Revised Unabridged Dictionary (1913)

Sponginess \Spon"gi*ness\, n.
   The quality or state of being spongy. --Dr. H. More.

Source : WordNet®

sponginess
     n 1: the porosity of a sponge
     2: the property of being able to occupy less space [syn: {compressibility},
         {squeezability}] [ant: {incompressibility}]