A printing system for applying a printing fluid to a substrate, comprising a printing fluid applicator and a recirculating printing fluid supply supplying printing fluid to the applicator, wherein the printing fluid comprising water and a water dispersible polyurethane additive of the general formula of (I) wherein Z is the central portion of a monomer unit that is the polymerization product of a diisocyanate; X1—Y1—X1 represents one or more soft segments wherein Y1 represents the central portion of a unit that is the polymerization product of a diamine or diol prepolymer having a molecular weight of greater than 300 Daltons; W is the central portion of one or more units containing an acid group; X2—Y2—X2 represents one or more hard segments wherein Y2 represents the central portion of a unit that is the polymerization product of a C2-C8 diol or diamine having a molecular weight of less than 250 Daltons; and X1, V and X2 can be the same or different and are an —O— or —N— atom; and further wherein the polyurethane additive has a weight average molecular weight of at least 6,000 Daltons and a sufficient number of acid groups to provide an acid number greater than 35, and the one or more X2—Y2—X2 hard segments are present at from 1 wt % to less than 13 wt % of the polyurethane additive.