Premix and method of preparing a thermally expandable and curable epoxy-based material

Premix two components for the preparation of a thermally expandable and curable epoxy-based material, comprising a component and a component B, wherein component A contains at least one isocyanate and component B contains at least one di- or polyol and wherein further at least one of components a or B contains at least one epoxy prepolymer, at least one of components a or B contains a heat-activatable hardener for epoxy prepolymers and at least one of the components a and B contains agent thermally activatable expanding.