An artificial fiber for use in an artificial grass sports field is disclosed wherein, seen in a transverse sectional direction of the fiber, at least part of the fiber is provided with a stiffness-enhancing portion extending in the longitudinal direction thereof. The artificial fiber includes at least two fiber flange portions, at least one fiber flange portion forming the stiffness-enhancing portion, while at least two fiber flange portions have a uniform thickness. The improved artificial fiber is less flexible and consequently exhibits less tendency to deform to a flat orientation, but does not increase the risk of injuries to players or have an adverse effect on the playing characteristics of the field. Also disclosed is an artificial grass lawn, suitable for sports fields, having a substrate to which one or more artificial fibers of the invention are attached.