I used a simple folding box design to test how well the felt could be cut, folded and joint to form a 3D object. I was looking for easy assembly, clean shapes, and a stable structure.
This design is copied from one featured in the book The Art of Cutting, credited to Josh Jakus.
As expected, this material doesn’t have enough rigidity to make a particularly stable box. However, I suspect felt only slightly thicker (e.g. 3 mm) would work OK.
This thicker felt works well, though the stiffness causes the box to deform at this small size. A larger box might work better.
This felt also works well, and can be worked so that the edges are sharp and the surfaces quite flat.
Box on the left has corner cutouts.
I tried another test cutting out circles around the 4 corners to allow for easier folding, but this didn’t seem to make a huge difference.