Cumulative mass of the fragment masses over their average filling factor φ. The mass is normalised by the total fragment mass m_tot. The collision velocities are v₀ = 10   m   s^-1 (top) and v₀ = 12.4   m   s^-1 (bottom). Compared to the initial distribution of filling factors (Fig. 1), the curves are shifted significantly towards higher filling factors. This reflects the compression taking place during the collision.