Type of filler particle used in packable composite:
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
Fibrous filler particles
Microcrystalline filler particles
Mixture of both
None of the above