FIELD: spirocyclic boric acid esters of the general formula: 
wherein R1, R2 are independently from each other are pentitol, hexitol, neopentyl glycol or pentaerythrite residues; Z is a guanidine, melamine, piperazine or ethylene diamine N- base, and m is an integer of 1 to 3, as a combustion inhibitor for polyolefins or polyurethanes. SUBSTANCE: polyolefins or polyurethanes are added in an amount of 5- 50% of the spirocyclic boric acid ester polymer. They can be added both to the final polymer and at the synthesis stage. EFFECT: improved properties of the combustion inhibitor and more efficient process for imparting fire resistance properties to the polymer. 3 cl, 2 tbl
