The invention relates to a process for the production of prefoamed poly(meth)acrylimide (P(M)I) particles which can be further processed to give foam mouldings or composites. A feature of this process is that a polymer granulate is first heated and thus prefoamed in an apparatus by means of IR radiation of a wavelength suitable for this purpose. Said granulate can be further processed in subsequent steps, e.g. in a press mould with foaming to give a moulding or a composite workpiece with foam core.