The Collaborative International Dictionary of English v.0.48:

energy-absorbing \energy-absorbing\ adj.
   capable of absorbing energy; as, energy-absorbing bumpers
   reduce injury and damage in vehicle collisions.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

energy-absorbing
    adj 1: (of a nuclear reaction) occurring with absorption of
           energy [syn: endoergic, energy-absorbing] [ant:
           energy-releasing, exoergic]