We have investigated the spatial variation of specific gravity (nonuniformities) in full size commercial pads for chemical mechanical polishing using a previously described nondestructive ultrasound transmission (UST) technique. After UST analysis, the different regions showing relatively higher and lower ultrasound permeability, which directly correlates with material density, were isolated and subjected to further evaluation of their mechanical properties using dynamic mechanical analysis (DMA) and tribological properties using a bench top chemical mechanical planarizdtion (CMP) tester. Though the evaluated regions did not show significant variation in their tribological properties, presence of such regions in the body of the polishing pads has the potential to induce intermittent process defect during the CMP process. (c) 2006 American Vacuum Society.