Hi-Tech Diamond sponge pads are to be used under diamond smoothing discs, Tech-11 polishing pads and final polishing pads to provide a cushion that helps remove flat spots from cabochons.. Simply peel the PSA backed sponge pad and apply to a clean backing plate. Then, apply your smoothing disc or polishing pad directly on top of the sponge pad. 6-inch- and 8-inch-diameter pads are available. All sponge pads are 1/8-inch thick and come with a PSA backing for easy application on backing plates.