expanded polystyrene
noun /ɪkˌspændɪd ˌpɒliˈstaɪriːn/
  /ɪkˌspændɪd ˌpɑːliˈstaɪriːn/
(also Styrofoam™ especially in North American English)
 [uncountable]- a form of polystyrene used for protecting objects in packages and for stopping heat, noise, etc. from escaping