Abstract: Nanocellular expanded polymer beads with cells have an average size less than 1 ?m, a relative density less than 0.25, wherein the relative density is the ratio between the density of the expanded polymer beads with respect to the density of the solid polymer beads, and a solid skin with a thickness less than 5 ?m. A method for manufacturing the beads by dissolution foaming of a foaming agent, use of the nanocellular expanded polymer beads for manufacturing a nanocellular polymeric material or a nanocellular powder, and the nanocellular polymeric material or nanocellular powder having the nanocellular expanded polymer beads are also related.