  We discuss the use of 3D printing to physically visualize (materialize) fluid
flow structures. Such 3D models can serve as a refreshing hands-on means to
gain deeper physical insights into the formation of complex coherent structures
in fluid flows. In this short paper, we present a general procedure for taking
3D flow field data and producing a file format that can be supplied to a 3D
printer, with two examples of 3D printed flow structures. A sample code to
perform this process is also provided. 3D printed flow structures can not only
deepen our understanding of fluid flows but also allow us to showcase our
research findings to be held up-close in educational and outreach settings.
