Critical mass-loss rate as a function of stellar radius from thermal considerations (see Eq. (9)). Solid lines show the critical mass-loss rate based on local thermal properties of the sub-surface layers of the donor star (see Eq. (8) and Fig. 3), whilst dashed lines show the critical mass-loss rate based on global thermal properties (see Eq. (6)). The linear portions of the curves correspond to the giant phases. The colours of the lines correspond to different initial donor masses, as indicated to the lower left of each dashed line.