The raw material properties and characteristics of four different microfibrillated celluloses (MFCs) produced by microfluidizing were investigated. The cellulose materials were never-dried and dried microcrystalline cellulose (MCC), a commercial MCC, and an enzymatic-mechanically treated softwood sulfite pulp. The study comprises extensive initial and final physical, structural, and molecular-level analyses. The results indicated that raw material properties related to both fibril aggregation, structural compaction levels and geometric heterogeneity and interaction levels essentially affected both the process and the final MFC properties. The increase in specific surface area (SSA) was minor for the enzymatic-mechanically treated raw material, while MCC showed a larger increase of several orders of magnitude in SSA. The drying of particulate MCC was reflected both in improved fibrillation efficiency and in the final MFC properties, primarily observed as enhanced SSA, in fibril dimensions and in gel strength. The feed consistency (7.5 %) applicable with dried, particulate MCC in fluidization was more than any of those hitherto reported. The study indicated that MCC can facilitate energy-efficient MFC production with the application of fluidization technology.