In a method of producing a thermosetting foam, a first of two foam forming blends ("A-Blend") is prepared using a multi-functional isocyanate such as polymeric polymethylene polyphenylisocyanate ("PMDI"). A second of two foam forming blends ("B-Blend") is prepared by mixing together a polyol; water; a tertiary amine catalyst having at least two hydrogen bonding sites for one molecule; and, an alkali metal organo-salt catalyst. The tertiary amine catalyst is of a type wherein both the hydrogen segment and the hydroxyl segment of water are attracted by both of the hydrogen bonding cites on the catalyst molecule essentially simultaneously. A first blowing agent is included with one of the two foam forming blends. When the first and second foam forming blends are mixed together, the tertiary amine catalyst quickly initiates a reaction predominately of the polymeric polymethylene polyphenylisocyanate with water (as opposed to a reaction with the polyol). The quick reaction of the PMDI with water causes, prior to a gel point of the foam, both (1) the production of a second blowing agent for forming cells in the blends and for causing expansion in the liquid blends; and (2) sufficient exothermic heat to initiate boiling of the first blowing agent. Relatively large amounts of alkali metal organo-salt catalyst induce rapid vaporizing of the first blowing agent due to a high level of exothermic heat, whereby expansion of the mixed blends is substantially completed prior to the effective conversion of the mixed liquid blends to a solid. According to the method, a degree of completion of expansion of the foam at any point in time exceeds a degree of completion of chemical reactions of the foam. In another mode of the invention, a frothing agent is also employed.