A novel method is disclosed to make cellulose filaments (CF) from wood or other plant fibers with lower energy consumption. The method consists of multi-stage, high consistency refining, followed by low consistency refining or by low consistency, non-refining mechanical treatment, of wood or other plant fibers. The total specific refining energy for the multi-stage, high consistency refining is preferably 2,000-18,000 kWh/t, and more preferably 2,000-12,000 kWh/t. The CF produced can be used as a superior reinforcement additive in the production of paper, tissue or paperboard and in the production of plastic composites. It can also be used as a viscosity or rheology modifier in food products, coatings or drilling muds. The CF produced can also be used to make strong films for application in packaging and in composites.