Sonobe is a type of modular origami that is named for its inventor, Mitsunobe Sonobe. The term is usually used to refer to a sonobe module, which is a basic unit used to construct all larger items. Like many other forms of origami, the basic unit is made using a square piece of paper. These units can be linked together to form a variety of shapes, and there are also variations on the basic unit that can be used to make even more shapes.
A sonobe module is fairly easy to make, but it can take many modules to make more complex designs. The basic unit is made using a square piece of paper, which is first creased in half with the plain side facing inward. Both edges of the paper parallel to the center crease are then folded in to meet the center crease.
Next, the top left corner must be brought across so that the top, or short side, of the resulting rectangle is aligned with the long right side of the rectangle, resulting in a diagonal crease. This crease is then unfolded, and the triangular creased portion of the right facing panel is folded under into the interior of the structure. The triangular portion created by the first crease is then folded under the right panel.
Turning the entire module around 180 degrees, the process is then repeated on the other half of the module. The resulting unit should have two pockets and two flaps and should be shaped like a parallelogram with 135- and 45-degree angles. While this process sounds complicated when explained verbally, it is actually quite simple when looking at a diagram. As such, the best way to learn is to look at a diagram and follow the directions carefully.
The way in which the sonobe modules are combined depends on the design being made. Pockets and flaps are utilized to hold the design together, and the resulting modular origami is often quite sturdy. For beginners, a cube made of six units can be fairly easily constructed. Using common sense and noting that all units meet at right angles, it is often possible to figure out how to build a cube without detailed directions.
More complex designs require more sonobe modules but similar skills. Commonly, intermediate enthusiasts choose to build a design called a stellated icosahedron, which requires 30 units. Using logic and one's imagination, it is possible to build quite complex and beautiful sonobe designs.