3D printing techniques provide simple ways to produce geometrically complex materials while reducing waste. Typically, objects made from polymeric (plastic) materials cannot be manipulated after 3D printing as the polymerisation process results in ‘dead’ polymer chains. Zhiheng Zhang, Nathaniel Corrigan and Cyrille Boyer from the UNSW Sydney, collaborating with researchers from the University of Auckland (New Zealand), have reported a significant breakthrough that tackles this problem by combining a ‘living’ polymerisation process with 3D printing (Zhang Z., Corrigan N., Bagheri A., Jin J., Boyer C. Angew. Chem. Int. Ed. 2019, 58, 17 954–63). The photomediated ‘living’ 3D printing process, based on the RAFT polymerisation process developed at the CSIRO, uses metal-free and non-toxic components in water and is activated by harmless green light irradiation. The polymeric materials can then be modified after 3D printing by performing successive polymerisations from the ‘living’ chains, which produces 3D printed objects with complex and tailorable chemical and physical properties. Additionally, by controlling the light irradiation, 4D printed materials (3D printed materials that respond to an external stimulus) can be formed, as demonstrated by 3D printed objects that reversibly folded when exposed to water. This process could facilitate the development of functional and stimuli-responsive 3D-printed materials for varied applications, including nanomedicine and other bioapplications.