A method of manufacturing an adhesive foamed product for use in a hollow component of a motorcar, includes the steps of mixing an adhesive resin, a foaming agent, a crosslinking agent, a foaming accelerator and a polymerizable monomer to thereby formulate a highly foamable composition, arranging the foamable composition thus formulated in the interior of a hollow component of a motorcar, and heating the foamable composition until it is foamed to have a shape corresponding substantially to the shape of the hollow component.