A reaction system for forming a viscoelastic polyurethane foam that has a resiliency of less than or equal to 20 % as measured according to ASTM D 3574, the reaction system comprising: an isocyanate component that includes at least one isocyanate, an isocyanate index of the reaction system being from 50 to 110; and an isocyanate-reactive component that is a mixture that is formed by adding at least a polyol component, an additive component, and a preformed aqueous polymer dispersant, the mixture including: from 50.0 wt% to 99.8 wt% of the polyol component, based on the total weight of the mixture, the polyol component including at least one polyether polyol, from 0.1 wt% to 49.9 wt% of the additive component, based on the total weight of the mixture, that includes at least one catalyst, and from 0.1 wt% to 6.0 wt% of the preformed aqueous polymer dispersant having a pH from 6.0 to 12.0, based on the total weight of the mixture, the aqueous polymer dispersant including from 5 wt% to 60 wt% of a polymeric component and from 40 wt% to 95 wt% of a fluid medium that includes at least water, the polymeric component including at least one base polymer derived from 20 wt% to 100 wt% of at least one hydrophilic acid monomer having at least one carbonyl group, phosphate group, phosphonate group, or sulfonyl group, and optionally derived from at least one hydrophobic terminally unsaturated hydrocarbon monomer, wherein the preformed aqueous polymer dispersant is a continuous liquid phase component at ambient conditions of room temperature and atmospheric pressure. an isocyanate component that includes at least one isocyanate, an isocyanate index of the reaction system being from 50 to 110; and an isocyanate-reactive component that is a mixture that is formed by adding at least a polyol component, an additive component, and a preformed aqueous polymer dispersant, the mixture including: from 50.0 wt% to 99.8 wt% of the polyol component, based on the total weight of the mixture, the polyol component including at least one polyether polyol, from 0.1 wt% to 49.9 wt% of the additive component, based on the total weight of the mixture, that includes at least one catalyst, and from 0.1 wt% to 6.0 wt% of the preformed aqueous polymer dispersant having a pH from 6.0 to 12.0, based on the total weight of the mixture, the aqueous polymer dispersant including from 5 wt% to 60 wt% of a polymeric component and from 40 wt% to 95 wt% of a fluid medium that includes at least water, the polymeric component including at least one base polymer derived from 20 wt% to 100 wt% of at least one hydrophilic acid monomer having at least one carbonyl group, phosphate group, phosphonate group, or sulfonyl group, and optionally derived from at least one hydrophobic terminally unsaturated hydrocarbon monomer, wherein the preformed aqueous polymer dispersant is a continuous liquid phase component at ambient conditions of room temperature and atmospheric pressure. from 50.0 wt% to 99.8 wt% of the polyol component, based on the total weight of the mixture, the polyol component including at least one polyether polyol, from 0.1 wt% to 49.9 wt% of the additive component, based on the total weight of the mixture, that includes at least one catalyst, and from 0.1 wt% to 6.0 wt% of the preformed aqueous polymer dispersant having a pH from 6.0 to 12.0, based on the total weight of the mixture, the aqueous polymer dispersant including from 5 wt% to 60 wt% of a polymeric component and from 40 wt% to 95 wt% of a fluid medium that includes at least water, the polymeric component including at least one base polymer derived from 20 wt% to 100 wt% of at least one hydrophilic acid monomer having at least one carbonyl group, phosphate group, phosphonate group, or sulfonyl group, and optionally derived from at least one hydrophobic terminally unsaturated hydrocarbon monomer, wherein the preformed aqueous polymer dispersant is a continuous liquid phase component at ambient conditions of room temperature and atmospheric pressure.