A continuous device (1) is provided for impregnating, in a single step, strands or ribbons of natural fibers (100) with a specific aqueous polymer dispersion to consolidate the fibers at the core of the fiber bundle and to improve their mechanical strength without any need for twisting. The device includes a stretching component (10) for elongating by the strand or the ribbon of natural fibers by stretching to give them a required yarn count, an impregnating component (20) for impregnating the fibers with the aqueous dispersion, a shaper for shaping/calibrating the wrung fibers, a dryer (40) for drying the shaped/calibrated fibers, and a conditioner (50) for conditioning the dried fibers to transform them into yarn or ribbon.