Abstract: In solid propellant rocket motors the size of the flowfield defined by the bore continually increases as the solid propellant is consumed. As a result, the efficacy of a rigid baffle decreases through the burn. By making the baffle flexible, it can be deformed to fit the small initial geometry and its expansion due to inherent resilience naturally accommodates the enlarging geometry of the propellant bore. Since the baffle is flexible, it can participate in the oscillations and thereby alter frequency and mode structure and also introduce nonlinear behavior. Thus, pressure waves propagating in one direction around the propellant bore lift a flap of the baffle and pass through the clearance. Pressure waves propagating in the other direction around the bore, however, press the flap against the surface of the bore to restrict the passage of such waves. As a result, the flexible baffle acts as a "check valve" to limit wave motion.