Evolutionary tracks of donor stars with metallicity ranging from Z = 0.0001 up to Z = 0.02 (similar to Fig. 2) as they evolve from the zero-age main sequence until they experience mass loss by Roche-lobe overflow (black outlined). Their subsequent evolution as stripped stars is highlighted in the inset panel. The low metallicity models are more compact and hotter before interaction. However, after mass transfer they are cooler and more luminous than the high metallicity stripped stars. A discussion of the evolution is provided in Sects. 4.1–4.3.