The Collaborative International Dictionary of English v.0.48:

Limpness \Limp"ness\, n.
   The quality or state of being limp.
   [1913 Webster] Limpsy

WordNet (r) 3.0 (2006):

limpness
    n 1: a flabby softness [syn: flabbiness, limpness,
         flaccidity]