Three-dimensional (3D)-printing techniques such as stereolithography (SLA) are currently gaining momentum for the production of miniaturized analytical devices and molds for soft lithography. However, most commercially available SLA resins inhibit polydimethylsiloxane (PDMS) curing, impeding reliable replication of the 3D-printed structures in this elastomeric material. Here, we report a systematic study, using 16 commercial resins, to identify a fast and straightforward treatment of 3D-printed structures and to support accurate PDMS replication using UV and/or thermal post-curing. In-depth analysis using Raman spectroscopy, nuclear magnetic resonance, and high-resolution mass spectrometry revealed that phosphine oxide-based photo-initiators, leaching out of the 3D-printed structures, are poisoning the Pt-based PDMS catalyst. Yet, upon UV and/or thermal treatments, photo-initiators were both eliminated and recombined into high molecular weight species that were sequestered in the molds.