The invention relates to a foamed isocyanate-based polymer derived from a reaction mixture comprising an isocyanate, an active hydrogen-containing compound, a blowing agent and a highly branched polysaccharide which is derivatized to provide a hydrophobicity which renders it compatible with a polyether polyol with which the underivatized polysaccharide is incompatible. Further the invention relates to a mix and a process for the production of isocyanate-based polymer. The mix for the production of a foamed isocyanate-based polymer comprises a mixture of the derivatized polysaccharide of the invention and an active hydrogen-containing compound. The process for producing a foamed isocyanate-based polymer comprises the steps of: contacting an isocyanate, an active hydrogen-containing compound, a derivatized highly branched polysaccharide and a blowing agent to form a reaction mixture and expanding the reaction mixture to produce the foamed isocyanate-based polymer. The derivatized highly branched polysaccharide of the invention has an active hydrogen functionality of at least 15 and comprises randomly bonded glucopyranose units, having an average number of 10-100 glucose residues.