Cockling of paper is unwanted out-of-plane deformation arising from variations in humidity. Paper is typically characterised by measurements of dimensional changes when slowly changing the humidity or by measurements of cockling on printed paper after printing. Here, a novel experimental set-up is presented in which cockling can be measured on-line at high speed in the inkjet printing process. Cockling was recorded as a function of time. It is shown that the cockling is several orders of magnitude higher during printing than after printing. Measurements on three papers are reported.