Watch How to Build a Robot Out of a Mushroom Growing Kit
If you're in one of those unique situations where you have to build a robot without a 3D printer or a foam board and have a mushroom growing kit laying around, this video by the YouTube channel Alta's Projects might be the inspiration you've been waiting for.
The YouTuber uses shiitake mushrooms to do this which is edible, easy to grow, and native to East Asia. It is considered a medicinal mushroom in some forms of traditional medicine, and as you can see in this video, they also make a good base for building robots. He builds the mushrooms in a mold and then cooks them to kill the fungi. The material he achieves is spongy but not compressible like styrofoam would be. The end result looks kind of goofy but works nicely which is all that matters.
If you're curious to learn how you can tackle a similar project, make sure to give this one a watch since the video is light, educational, and entertaining at the same time. Enjoy!