Presented herein is a report on a wire-damping device which has shown considerable damping ability when placed in a hollow rotor blade. A series of tests is reported which have all shown the damping ability of this device at nonrotating and rotating conditions. Two theories are postulated and expressions derived to explain the mechanism of damping by the wires for nonrotating-type damping and rotating-type damping. The postulated mechanism for damping in the nonrotating rotor blade considers that the wires absorb energy by rubbing around one another as a result of the motion imparted by the vibratory motion of the blade. The postulated mechanism for damping in the rotating rotor blade considers that a component of centrifugal force holds the wires against the side of the blade and the vibratory bending motion of the blade causes relative motion between the blade wall and the adjacent wires to absorb energy. Criteria are set forth for determining which mechanism is operative. Good correlation was obtained between test and theory.