Dependence of the volume filling factor on impacting projectiles; 1a), 2a): low filling factor aggregates φ = 0.14 generated by sub m/s impacts; 1b): change of original target upon collisions with 0.25 mm aggregates at 6 m/s; 2b): change of original target upon collisions with 1.2 mm aggregates; The transition zone is only on the order of up to several mm. It separates two protoplanetesimal zones with filling factors characterized by the process by which they formed, i.e. a core-shell particle with highly porous core and dense shell forms.