Pebble mass fraction in the resulting planetesimals for simulations with, initially, cm-sized pebbles, as a function of the planetesimal radius, R_solid. Particles are defined as pebbles if they have radii a> 1 mm. For more massive planetesimals the collision speeds are larger and the collisions can then result in fragmentation, decreasing the pebble mass fraction. However, massive clouds do not have time to virialize after each collision and the particles will move with subvirial speeds (see Fig. 5). This causes the number of fragmenting collisions to decrease as the collapse goes on, ensuring that a fraction of the primordial pebbles survive even in the most massive planetesimals.