A process for the preparation of thermoplastic auxetic foams comprising the steps of: a) taking conventional thermoplastic foam; b) subjecting said foam to at least one process cycle wherein the foam is biaxially compressed and heated; c) optionally subjecting the foam to at least one process cycle wherein the biaxial compression is removed and the foam mechanically agitated prior to reapplying biaxial compression and heating; d) cooling said foam to a temperature below the softening temperature of said foam; and e) removing said compression and heat.