Compositions are provided including an uncrosslinked thermoplastic nitrogen-containing matrix material and composite particles distributed in the matrix material. The composite particles each include a chemical blowing agent particle encapsulated within a shell including an uncrosslinked thermoplastic material. The uncrosslinked thermoplastic material exhibits at least a certain minimum complex viscosity at a decomposition temperature of the chemical blowing agent particle. Also described are foam compositions and articles including the foam compositions, such as a sheet or multilayer construction. Composite particles are further provided. Methods of making the foam compositions are additionally described herein. Also, polishing pads, polishing systems, and methods of polishing a substrate are provided.