Most 3D printers operate entirely open-loop. In other words, a computer tells them where to place material but the system doesn’t check that material was actually deposited. With non-traditional printing materials, often times the materials exhibit erratic behavior. In order to get acceptable printing results with these tricky materials, closed-loop printing approaches are necessary to compensate for a variety of naturally occurring errors during the printing process. I used lasers to monitor the shape of the part mid-print and developed algorithms for correcting shape errors during prints. The technique enabled printing parts with high geometric fidelity despite uncertainty in the material behavior and environmental conditions.