PURPOSE: To obtain the titled low-smoking foam, by reacting a phenolic polyol resin containing isocyanuric acid (formaldehyde adduct) with an organic polyisocyanate in the presence of a blowing agent, a colorant, etc.

CONSTITUTION: The following components are mixed together: (A) 100pts.wt. phenolic polyol resin prepared by reacting phenol with an aldehyde, (B) 1.5W 20pts.wt. isocyanuric acid and/or its aldehyde adduct of the formula (wherein l, m, and n are each 0W2), (C) a blowing agent (e.g., trichloromonofluoromethane), (D) a catalyst (e.g., dibutyltin dilaurate) and (E) a surfactant. The titled modified polyurethane foam of excellent flame retardancy is obtained by mixing and reacting the above-produced mixture with an organic polyisocyanate (e.g., 4,4'-diphenylmethane diisocyanate).