Here's a pretty simple but effective multi-material plug I designed to fit in the holes on the side of the Snapmaker U1 when you don't install (or have removed) the spool holders. The lack of a multi-material / multi-toolhead model library needs to be fixed! In the meantime, this is a good example of how something simple could be improved with inclusion of a flexible material.

I printed @martymaker's Scratch Maker: Box Cutter (https://makerworld.com/en/models/669599-cat-scratch-maker-box-cutter-now-in-more-sizes#profileId-597254) and realized there weren't many good designs for the cardboard strips it produced. As a result I decided to waste too much time in Tinkercad and about 3 kilos of filament before I was happy with the final product.