The method of preparation, determination of foaming parameters, and methods for the determination of physicochemical properties of polyurethane-polyisocyanurate (PUR-PIR) foams prepared with the use of N,N'-di(methyleneoxy-2-hydroxyethyl)urea and boric acid derivatives are presented in this paper. It was found that application of the borate as a polyol component and simultaneously as a flame retardant in the recipe for production of PUR-PIR foams was very favorable. The foams prepared were characterized by reduced brittleness, higher compressive strength and content of closed cells, as well as considerably lower flammability in comparison with standard foam. The results show that the new polyol prepared on the basis of N,N'-di(methyleneoxy-2-hydroxyethyl)urea and boric acid can be applied for production of rigid PUR-PIR foams, and it improves their physicochemical properties. (C) 2010 Wiley Periodicals, Inc. I Appl Polym Sci 118: 2250-2256, 2010