The method of boroorganic compounds preparation by esterification of boric acid and glycols has been presented. The obtained compounds tri(2-hydroxybutyl)borate, tri(hydroxythiodiethylene)borate, tri[(3-chloro-2-hydroxy-1-propoxy)-1-methylpropyl]borate, and tri[(3-chloro2-hydroxy-1-propoxy)thiodiethyl]borate were used to produce the rigid polvurethane-polyisocyanurate (PUR-PIR) foams. The foams ere prepared by one-stage method and the amount of borates added varied, within the range from 0.0 to 0.4 of chemical equivalent. The method of preparation, determination of foaming parameters, and methods of testing of the physicochemical properties of PUR-PIR foams as well as their results have been presented. A special emphasis was put on reduction of the foam flammability. It was found that application of the obtained compounds as polyolic components has a favorable effect on the properties of the produced rigid PUR-PIR foams. The obtained rigid PUR-PIR foams were characterized by a higher compressive strength, lower brittleness, considerably reduced flammability, and higher content of the closed cells. (c) 2006 Wiley Periodicals, Inc.