Process for production of foam webs or foam sheets, these webs or sheets being based on a polymer selected from polysulfones, polyetherimides, polyether ketones, and styrene polymers, via extrusion of a melt which comprises the polymer and a blowing agent, and then foaming of this melt, which comprises a process in which the melt also comprises from 1 to 50% by weight, based on the polymer, of a filler selected from A) a fibrous filler A, B) a particulate, non-graphite filler B, and mixtures of these.