Abstract: Exemplary fibers of the invention, useful for reinforcing hydratable cementitious materials such as concrete and mortar, have three-dimensional twist curvatures. Preferably, the fibers are flat or flattened and have first and second opposed flat or flattened ends that are twisted out of phase, and which preferably define therebetween an intermediate elongate fiber body having a curvature in more than one direction. Processes of the invention comprise forming a fiber with a three-dimensional twisted shape by twisting at least two fibers together to form a twisted fiber bundle to impart a twist curvature into the fiber material. The twisted fiber bundle can then be cut into separate fibers or stored on bobbins for shipment to another location for cutting. Advantages of the invention include enhanced dispersibility of the fibers in hydratable cementitious compositions.