This study starts with a literature review on SLS-printed PA12 and how its ductility is influenced in the printing process as well as by post processing. The rest of the study focuses on one particular post processing technique, heat treatment under isostatic pressure, including an experimental phase to gain insight into the influence of this post processing method on the ductility of SLS-printed PA12. A thesis submitted in partial fulfilment of the requirements for the degree Master of Science in Polymer Engineering. Presented to the Department of Engineering & Design Windesheim University of Applied Sciences, September 30th 2020.