This invention relates to hybrid polymer polyols. These hybrid polymer polyols comprise the free-radical polymerization product of (A) a base polyol comprising (1) a polymer modified polyol selected from (a) dispersions of polyureas and/or polyhydrazodicarbonamides in a hydroxyl group containing compound and (b) polyisocyanate polyaddition polyols, and (2) optionally, a polyol having a functionality of 2 to 6 and an OH number of from 20 to 500; (B) optionally, a preformed stabilizer; and (C) one or more ethylenically unsaturated monomers, in the presence of (D) a free-radical polymerization initiator, and (E) optionally, a polymer control agent. The present invention also relates to a process for the preparation of these hybrid polymer polyols, foams prepared from these hybrid polymer polyols and to a process for the preparation of these foams.