Process for preparing a polyol comprising particulate material in dispersed form by reacting an MDI-based polyisocyanate and a polyol having an equivalent weight of up to 400 in a relative amount such that the number of NCO-groups is 70-100% of the number of OH-groups in said polyol having an equivalent weight of up to 400, the reaction being carried out in a polyol having an equivalent weight of 500 or more. The polyols are claimed as well.