The invention relates to a method and to a device for manufacturing polymer foam beads or balloons. This method comprises the following steps: a) forming liquid beads with an organic phase, or liquid balloons by encapsulating an aqueous phase W.sub.1 in an organic phase; b) suspending the liquid beads or balloons in an aqueous phase W.sub.2; c) subjecting the emulsion thus formed to a temperature .theta. that is at least equal to the temperature at which said initiator has a decomposition half-life of 5 to 15 minutes, but that is lower than the degradation temperature of the organic phase, for the time required for this phase to gel; and d) completing the solidification of the organic phase. Applications: manufacture of microballoons used especially for producing targets for the study of inertial confinement fusion, matrices intended for solid-phase syntheses, the specific immobilization of biological components of the protein type, or else the execution of high-throughput biological tests.