## Introduction: How to Make a Triangular Hexahedron Out of Paper (Sonobe Units)

About the Process

The art of modular origami (paper folding with multiple pieces of paper, often used to create 3D geometric shapes) has been enjoyed by all ages. It is an extremely diverse field, consisting of many models, from figures that can be made with 2 pieces of paper, to elaborate models assembled from over 100 "modules," or building units.

Many different unit styles have been invented, each resulting in a different assembly technique. The model in this guide uses Sonobe units--a building module named after its presumed creator, Mitsunobu Sonobe. They are easy to fold, and models constructed with them are generally very sturdy and should not need any glue to stay together.

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The Model

This guide instructs on the creation of a 3D geometric shape called a "triangular hexahedron," which is the simplest figure that can be constructed from Sonobe units. It will walk through the steps to make a single unit and continue on to the assembly of the model. The finished product looks like two 3-sided pyramids joined together at the base, and depending on the size of the paper used, the model may be bigger than a basketball or smaller than a pencil eraser.

## Step 1: Supplies

Supplies needed:

- 3 square pieces of paper of the same size (post-it notes are not always an exact square, but they work.)

- A hard, flat surface to make folding easier and cleaner

- Optional: Coloring supplies if using white paper (crayons, markers, colored pencils, etc.)

## Step 2: Other Notes

- If you are using white paper and want color in your model, now is the time to add it. Add your colors, design, or drawing to one side of the paper. The colored side should be facing downwards when making the unit.

- If using sticky post-it notes, start with the sticky side facing downwards.

- Remember, precision is important when making those folds!

## Step 3:

You will be using 3 squares to make 3 units, so you may want to go through the steps with each sheet as you go on.

Take one piece of paper and fold it in half.

Unfold it.

## Step 4:

Fold the edges to the middle line created in the previous step.

Unfold.

## Step 5:

Fold the bottom left corner so its edges line up with the lines created in the previous step.

Rotate the sheet and repeat the fold on the opposite diagonal corner.

## Step 6:

Fold the triangle shape in the bottom left corner until its edge lines up with the bottom line.

Rotate the sheet and repeat on the other corner.

## Step 7:

Fold the edges to the middle.

## Step 8:

Take the bottom right corner and fold it until it touches the middle of the top edge. You will know you did it correctly if the two edges align perfectly, resulting in a sharply-pointed corner.

Rotate the shape and repeat the step with the other corner.

## Step 9:

Insert the corner from one of the "triangles" all the way into the "pocket" as shown in the picture. Rotate the shape and repeat the step on the other corner.

Opening the model slightly by inserting your thumb into the pocket (or a pencil tip with very small units) may make it easier to complete this step. The unit should lie flat once both corners are tucked.

Turn it over.

## Step 10:

Turn the unit until one of the sharp points is pointed slightly to your right, as in the picture.

## Step 11:

Fold the sharp bottom point to the blunt corner on the top right.

Turn the unit and repeat the step on the other side. Unfold.

## Step 12:

You have a completed Sonobe unit.

## Step 13:

Once you have three complete units, you are ready to build a triangular hexahedron.

The units will be numbered from here to avoid confusion.

1. Blue

2. Yellow

3. Pink

## Step 14:

Take unit 1 and make note of its "pockets," indicated in the picture with solid red.

## Step 15:

Insert one of the points of unit 2 into a pocket on unit 1.

## Step 16:

Insert a point of unit 3 into the empty pocket on unit 2.

## Step 17:

Insert the last point of unit 1 into the unused pocket on the unit 3. You may have to bend the point to get it into the pocket.

## Step 18:

The model so far should look like one corner of a cube.

## Step 19:

Turn the model so the inside of the "cube" is facing you.

## Step 20:

Take the point of unit 1 and insert it into the pocket of unit 2 behind the cube's left "wall." You will have to bend the "wall" to do this.

Make sure the remaining two points are not on the inside of the model.

## Step 21:

Insert the point of unit 3 into the last pocket of unit 1.

## Step 22:

Carefully slide the last point of unit 2 into the last pocket of unit 3.

## Step 23:

Congratulations! You have completed the triangular hexahedron. It is a sturdy model that can be thrown around with little damage and is also usable as a desk decoration, a small giftbox (with larger units), or even as a jewelry component (with very small units). Have fun and get creative!