The invention relates to a curable volume expandable polymer composition comprising an organic acid component, wherein the organic acid component comprises a first organic acid, a second organic acid, and optionally one or more additional organic acids; wherein said polymer composition, when being heated to an activation of expansion temperature above room temperature, undergoes volume expansion. When the organic acid component is heated to the activation of expansion temperature, the first organic acid and/or the second organic acid and/or the optionally present one or more additional organic acids decarboxylate and thus release carbon dioxide. The polymer composition traps the thus released carbon dioxide thereby causing the polymer composition to undergo volume expansion.