Recovery times and/or airflow of flexible polyurethane foam is increased by including certain tackifiers in the foam formulation. The tackifiers are characterized in being incompatible with polyol or polyol mixture used to make the foam, having a viscosity of at least 5,000 centipoise at 25 #C and having a glass transition temperature of at most 20 #C. The tackifier is pre-blended with certain monols to form a lower-viscosity blend that is combined with one or more other polyols and a polyisocyanate to form a reaction mixture for producing a polyurethane foam.