Mass transfer evolution in binaries with a 25 M_⊙ primary (initial mass), compared between the three different metallicities. Top panels: mass-transfer rate, bottom panels show the mass of the envelope (hydrogen content X_H > 10⁻³). Different colors correspond to different mass ratios between the binary components q = M₂/M₁, varying from 0.1 and 1.5 (the donor stays the same). Bold part of each curve indicates when the donor overflows its Roche lobe. In each case, the initial RLOF takes place when the primary radius is around R_RLOF ≈ 90 R_⊙, see the radius-age diagram on the right-hand side. In models with q ≤ 0.225 (not shown in the figure) the mass transfer became dynamically unstable. Models terminate at the end of core-He burning.