From The Collaborative International Dictionary of English v.0.48 :
nonrigid \nonrigid\ adj. (Aeronautics) Not rigid; especially, designating an airship having a shape maintained only by internal gas pressure and without a supporting structure. Opposite of rigid. [WordNet 1.5]From WordNet (r) 3.0 (2006) :
nonrigid adj 1: designating an airship having a shape maintained only by internal gas pressure and without a supporting structure [ant: rigid]