Polyolefinic particle foams containing additives may be produced by a process, which comprises(a) initially charging a pressure-resistant reactor with a dispersion consisting essentially of polyolefin particles and a liquid dispersion medium, and also a mixture of a volatile organic blowing agent and the additive to be introduced;(b) carrying out a heat treatment in which the polyolefin particles are impregnated with the mixture; and subsequently(c) discharging the dispersion through an orifice into a low-pressure space, thus foaming the polymer particles.The process achieves efficient incorporation of the additives into the polyolefin particles. The particle foams thus-obtained are useful for the production of moldings.