A polyisocyanurate foam insulation product is produced from an isocyanate component, a polyol-containing component, and a blowing agent. The polyol-containing component includes a first polyol and a second polyol, a fire retardant, and one or more surfactants, wherein the first polyol and the second polyol have different hydroxyl numbers, or have different functionalities, or differ in both hydroxyl number and functionality. In some formulations, the polylol-containing component may include a fire retardant, a metallo-organinc compound, or combinations thereof. The cell size of the foam may be less than 120 microns. The polyol-containing component may include a mixture of polyols having different functionalities.