PIPA polyols are made by reacting a low equivalent weight polyol with a polyisocyanate in the presence of a stabilizer. Low amounts, if any, of water are present. Useful stabilizers include functionalized linear or branched polyethers having at least one polyether segment having a molecular weight of 200 to 8000, wherein the functionalized polyether is terminated at one end with one or more isocyanate groups or with one or more isocyanate-reactive groups linked to the polyether through one or more urea and/or urethane groups, and further wherein all or a portion of such functionalized polyether contains one or more biuret, isocyanurate, urea or allophonate groups.