An inkjet printing system includes an inkjet printer responsive to digital signals and containing an ink composition having: (a) water, (b) dispersed pigment particles, (c) a humectant, and (d) a polyurethane additive having at least a first soft segment having siloxane groups, the additive having a weight average molecular weight of at least 10,000 daltons and a sufficient number of acid groups to provide an acid number greater than 60. An improved combination of scratch resistance and jetability is obtained.