A method of making a flexible polyurethane foam, comprising reacting, at an isocyanate index of 60 to 110; A) a polyol or mixture of alcohols that includes at least one polyol, wherein the polyol or mixture of alcohols (i) has a hydroxyl number of less than 270, (ii) has a number average hydroxyl functionality of 2 to 4; (iii) includes at least one polyether polyol that has a hydroxyl number of less than 170 and (iv) has an oxyethylene content of at least 10% by weight and/or includes at least one polyether polyol that contains at least 40% by weight oxyethylene units; and B) 1 to 5 parts by weight water per 100 parts by weight of component A), with C) at least one organic polyisocyanate, in the presence of D) at least one catalyst for the reaction of an isocyanate group with water and/or an alcohol; E) at least one foam stabilizing surfactant; and F) 1 to 45 parts by weight of a tackifier per 100 parts by weight of component A) wherein (i) the tackifier is at least partially incompatible with component A); (ii) the tackifier has a viscosity of at least 10 Pa·s (10,000 centipoise) at 25°C, measured using a rheometer, (iii) the tackifier has a glass transition temperature of at most 15°C, as measured by dynamic mechanical analysis with glass transition temperature taken as the temperature of the peak tan delta value using the test conditions described in the description, and (iv) the tackifier is not reactive with any of components A), B) and C). A) a polyol or mixture of alcohols that includes at least one polyol, wherein the polyol or mixture of alcohols (i) has a hydroxyl number of less than 270, (ii) has a number average hydroxyl functionality of 2 to 4; (iii) includes at least one polyether polyol that has a hydroxyl number of less than 170 and (iv) has an oxyethylene content of at least 10% by weight and/or includes at least one polyether polyol that contains at least 40% by weight oxyethylene units; and B) 1 to 5 parts by weight water per 100 parts by weight of component A), with C) at least one organic polyisocyanate, in the presence of D) at least one catalyst for the reaction of an isocyanate group with water and/or an alcohol; E) at least one foam stabilizing surfactant; and F) 1 to 45 parts by weight of a tackifier per 100 parts by weight of component A) wherein (i) the tackifier is at least partially incompatible with component A); (ii) the tackifier has a viscosity of at least 10 Pa·s (10,000 centipoise) at 25°C, measured using a rheometer, (iii) the tackifier has a glass transition temperature of at most 15°C, as measured by dynamic mechanical analysis with glass transition temperature taken as the temperature of the peak tan delta value using the test conditions described in the description, and (iv) the tackifier is not reactive with any of components A), B) and C). (i) the tackifier is at least partially incompatible with component A); (ii) the tackifier has a viscosity of at least 10 Pa·s (10,000 centipoise) at 25°C, measured using a rheometer, (iii) the tackifier has a glass transition temperature of at most 15°C, as measured by dynamic mechanical analysis with glass transition temperature taken as the temperature of the peak tan delta value using the test conditions described in the description, and (iv) the tackifier is not reactive with any of components A), B) and C).