Sonobe units are fun and very versatile. They can be used to make lots of shapes, from a pretty standard icosahedron to larger buckyballs and tori.

They can also be used to make square-er things.

This is a level 1 Menger Sponge, which is a pretty cool fractal. (It’s the 3-dimensional version of the Cantor set, for the mathematically inclined.) But if you can make this, then clearly the next step is to try a level 2. That’s not crazy, right?

Menger Sponges are a fairly common model to make from business cards, and I’ve found some versions made from a few other types of units as well. There are also a quite a few from Sonobe units, though (if I remember correctly) there were a lot fewer on the internet when I tried this (about 6 years ago).

Anyway, it turns out this is a little bit crazy. Sonobe units can make shapes based on cubes, but when the units lie completely flat, there’s very little to hold them together. This makes larger models very prone to just completely sliding apart when you try to move them. This is especially true with the paper I decided to use, which is rather thin. (Another option would be to use glue to hold it together, but that always makes me feel like I’m cheating.) But the best way to learn this is to try it, and that’s what I did.

Step one: fold lots and lots of units. (1056 total: I used 384 yellow, 192 blue and 480 pink.) Luckily they’re fairly simple and after a couple hundred, you get the hang of folding them quickly. Sometimes you can also recruit friends to help.

Cats like to help too, but sometimes they just get sleepy. Step two: assemble lots and lots of units.

You can see how loosely the units stay together here, especially when they’re only partly assembled.

Keep going… The 2×3 rectangles are probably the weakest parts, just because they’re flat. At least those are on the outside though, so they’re easy enough to fix; when the inner pink ones start getting loose, it’s nearly impossible to get your fingers inside to fix them without pushing apart other sections.

Once finished, it’s not something that you can move very much, or very easily. It would probably be sturdier if I had used thicker paper; the sheets I used were like post-it notes, but flimsier. If you get it situated on a shelf though, it looks nice… as long as nobody touches it.

Stay tuned for a post about another Menger sponge variation.