Type of filler particle used in packable composite:
Fibrous filler particles
Microcrystalline filler particles
Mixture of both
None of the above
Specifically the packable/condensable characteristics are derived from the inclusion of elongated, fibrous filler particles of about 100 µm in length and/or rough-textured surfaces or branched geometries that tend  to interlock and resist flow.
Phillips Dental materials 12th edition pg no 286