The present invention provides methods of manufacturing a chemical mechanical polishing (CMP polishing) layer for polishing substrates, such as semiconductor wafers comprising providing a compositionof a plurality of liquid-filled microelements having a polymeric shell; classifying the composition via centrifugal air classification to remove fines and coarse particles and to produce liquid-filledmicroelements having a density of 800 to 1500 g/liter; and, forming the CMP polishing layer by (i) converting the classified liquid-filled microelements into gas-filled microelements by heating them,then mixing them with a liquid polymer matrix forming material and casting or molding the resulting mixture to form a polymeric pad matrix, or (ii) combining the classified liquid-filled microelements directly with the liquid polymer matrix forming material, and casting or molding.