A reaction system for forming a polyurethane foam includes an isocyanate component that has at least one isocyanate and an isocyanate-reactive component that is a mixture formed by adding at least a polyol component, an additive component, and a preformed aqueous polymer dispersion. The mixture includes, based on the total weight of the mixture, from 50.0 wt % to 99.8 wt % of a polyol component including at least one polyether polyol, from 0.1 wt % to 50.0 wt % of an additive component including at least one catalyst, and from 0.1 wt % to 6.0 wt % of a preformed aqueous polymer dispersion. The preformed aqueous polymer dispersion has a solids content from 10 wt % to 80 wt %, based on the total weight of the preformed aqueous polymer dispersion, and is one of an aqueous acid polymer dispersion or an aqueous acid modified polyolefin polymer dispersion in which the polyolefin is derived from at least one C2 to C20 alpha-olefin.