The brake caliper piston plays a key role in caliper function, taking significant responsibility for qualities such as fluid consumption, insulation of the brake fluid from heat, seal rollback function, and brake torque variation sensitivity to disc thickness variation. It operates in a strenuous environment, being routinely subjected to high stresses and elevated temperatures. Given all of the demands on this safety-critical component (strength, stiffness, wear resistance, stable friction against rubber, thermal stability, machinability, manageable thermal conductivity, and more), there are actually relatively few engineering materials suitable for use as a caliper piston, and designs tend to be limited to steel, aluminum, and engineered plastics (phenolic composites). The lattermost - phenolic composites - has been of especial interest recently due to mass savings and possible reduction in brake corner judder sensitivity to disc thickness variation. This paper focuses on characterizing two important mechanical characteristics, stiffness and damping, of the most common piston materials, steel and phenolic. Data are shown first suggesting the effect of piston material on brake performance, and then stiffness and damping data from different methodologies are presented. From these data, a preferred methodology is recommended and results are reconciled with brake corner subsystem performance and modeling.