Polymer-modified polyol, for use as a starting material for polyurethane foam, is made by reacting an olamine, such as triethanolamine, with an isocyanate in the presence of a metal organic catalyst. The catalyst is a metal salt of an organic acid and the viscosity of the polymer-modified polyol is at least 2250 mPa·s. In one embodiment the catalyst is of the formulat M(O.CO.R.CH3)2 where M is a metal and R is a carbon chain of 6 to 20 carbons. A metal salt of a monohydroxy fatty acid, particularly ricinoleic acid may be used.