A blade of a rotor for a rotary-wing aircraft is equipped with an outer covering extending along the span of the blade. This outer covering is provided with an extrados skin and with an intrados skin defining a cavity. The blade also includes a structure that extends into the cavity and connects the blade to a hub of the rotor. The cavity is filled with a filling material that includes at least one partition parallel to a chord of the blade and at least two independent blocks of filling material filling the cavity, thereby allowing the reduction of the torsional rigidity along the span of the blade.