Abstract: Rigid polyisocyanurate foams are prepared by reacting together an organic polyisocyanate, a blowing agent, a trimerization catalyst, and a minor amount of a polyol, the polyol comprising a sufficient proportion of at least one polyoxyalkylene polyol having (i) terminal oxypropylene oxide blocks, (ii) a molecular weight of from about 300 to 3000, and (iii) an average hydroxyl functionality of from about 2 to 5 to form a foamed polyisocyanurate whose gel time is greater than about 70 seconds and friability is less than about 20 percent, as measured by the ASTM C-421 friability test. Laminates of such foams exhibit a high degree of fire resistance, low foam friability and good facer adhesion.