The Collaborative International Dictionary of English v.0.48:

noncollapsable \noncollapsable\ noncollapsible
\noncollapsible\adj.
   1. not able to be folded into a compact form. Opposite of
      collapsible. [Narrower terms: nontelescopic,
      nontelescoping]
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

noncollapsible
    adj 1: not capable of collapsing [syn: noncollapsible,
           noncollapsable] [ant: collapsable, collapsible]