The present application relates to a thermally expandable composition containing at least one peroxide cross-linking polymer, at least one peroxide, at least one polysaccharide and at least one endothermic, chemical blowing agent; as well as to shaped bodies containing said composition and to a method for sealing and filling voids in components, for strengthening or reinforcing components, in particular hollow components, and for bonding mobile components using shaped bodies of this type.