Who doesn’t love 3D Geometry that you can fold up? Follow the link to download the pdf so you can fold your own!
If you’ve spent anytime at all with circles, you’ve noticed that it’s very easy to fold a hex grid. Circles were built for this. But where, you ask, do the curves come from? Easy — the edge. Circle’s only got the one. Look at the CP and note where the curves begin and end. Now, fold the edge over, so it connects the two points. See? Just bend the paper a little and start pinching in the curve. As you practice this, you’ll see how much more accurate your lines will become. [via] – Link