Vi Hart is amazing with flexagons [0].<p>[0] <a href="https://www.youtube.com/watch?v=VIVIegSt81k" rel="nofollow">https://www.youtube.com/watch?v=VIVIegSt81k</a>
I made some tetra-tetra-flexagons for my wedding, and in the process made an ImageMagick script to take four images and turn them into two, one for each side of the sheet of paper.<p><a href="https://www.timpark.org/making-a-tetratetraflexagon/" rel="nofollow">https://www.timpark.org/making-a-tetratetraflexagon/</a> (unfortunately some of the external links are broken, I should do some editing)
The Hexaflexagon unit from "Things of Science" (June 1960):<p><a href="http://underlandia.com/index.php/2017/07/17/things-of-science-236-hexaflexagon/" rel="nofollow">http://underlandia.com/index.php/2017/07/17/things-of-scienc...</a>
I still have a 24-faced hexaflexagon I made in 1975, using onionskin paper and an HP plotter. (Thinness and accuracy are critical for high-order flexagons.)