The near surface region of polypropylene was hardened in a forming process, which involved a large shear strain in a strong thermal gradient. The optimal processing conditions were estimated by modeling the temperature distribution in the deformation zone. Microindentation testing was used to characterize the corresponding depth-dependent mechanical properties. The mechanical gradient, which developed after forming, was consistent with the observed variation in microstrucfture. (C) 2007 Wiley Periodicals, Inc.