Pellets, beads, particles, or other pieces of a thermoplastic elastomer having a maximum size in at least one dimension of 10 mm or less (collectively, “pellets”) are infused with a supercritical fluid in a pressurized container, then rapidly depressurized and heated either by immersion in a heated fluid or with infrared or microwave radiation to foam the pellets The pellets are prepared with at least two different densities. Pellets with different densities, thermoplastic elastomer compositions, or foam response rates are placed in different areas of a mold. The mold is filled with pellets, then the pellets are molded into a part. The part has areas of different density as a result of the placement of pellets of different density.