Mass fraction of helium in the donor at two different times. Top panel: Helium mass fraction at the beginning of the simulation showing no mixing. Bottom panel: Mixing of helium in the donor just before the explosion of the accretor. The red line shows a contour of ρ = 10⁴ g cm⁻³. During the accretion and inspiral the helium from the surface seeps into the deeper layers of the donor.