The melting process of a paraffin wax (n-octadecane) is studied in this work. A cubical test cell (40 x 40 x 40 mm(3)) with one heated and one cooled sidewall is applied. Using non-intrusive particle image velocimetry, the velocity field of the liquid phase region is evaluated. This field is decisively influenced by natural convection. In addition, the liquid fraction and the solid-liquid interface shape are reported and the impact of insulating the test cell is visualized. Mean velocities are calculated for several instants of time. The experimental data is provided with the purpose of validating numeric models. Therefore, the raw data of the phase front positions and the velocity fields are made available alongside this report. In addition, a study of the experimental uncertainties is provided. (C) 2019 Elsevier Ltd. All rights reserved.