Composition encountered by the forward shock wave as it moves (from left to right) through the winds of 25 M_⊙ (left) and 60 M_⊙(right) rotating stars. The shock wave starts at M_Exp = 10 M_⊙and 14.8 M_⊙, respectively, and the ST phase sets in when a mass M_S1 = M_Exp has been swept up and has presumably been well mixed. The quantities displayed correspond to the mass integrated composition of the wind, starting at M_Exp.