The Collaborative International Dictionary of English v.0.48:

nonadsorbent \nonadsorbent\, nonadsorptive \nonadsorptive\adj.
   lacking capacity to adsorb or cause to accumulate on a
   surface. Opposite of adsorbent.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

nonadsorptive
    adj 1: lacking a capacity to adsorb or cause to accumulate on a
           surface [syn: nonadsorbent, nonadsorptive] [ant:
           adsorbent, adsorptive, surface-assimilative]