Sonobe

Examples of modular origami made up of Sonobeflat equilateral triangle (two "faces", three edges);
unitsthe protruding tab/pocket flaps are simply
The Sonobe module is a unit used to build modularreconnected on the underside, resulting in two
origami, created by Mitsonobu Sonobe.triangular pyramids joined at the base.
Each individual unit is folded from a square sheetBuilding pyramids on a tetrahedron results in a
of paper, of which only one face is visible in thecube (the central fold of each module lays flat).
finished module; many ornamented variants of theThe same construction for an icosahedron (20
plain Sonobe unit that expose both sides of thefaces, 30 edges) requires 30 Sonobe units.
paper have been designed.Uniform polyhedra can be adapted to Sonobe
The Sonobe unit has the shape of a parallelogrammodules by replacing non-triangular faces with
with 45 and 135 degrees angles, divided bypyramids having equilateral faces; for example by
creases into two diagonal tabs at the ends andadding pentagonal pyramids pointing inwards to
two corresponding pockets within the inscribedthe faces of a dodecahedron a 90-module ball can
center square. The system can build a wide rangebe obtained.
of three-dimensional geometric forms by dockingArbitrary shapes, beyond symmetrical polyhedra,
these tabs into the pockets of adjacent units.can also be constructed; a deltahedron with 2N
The most popular intermediate model is thefaces and 3N edges requires 3N Sonobe modules.
stellated icosahedron, as shown in one of the twoThere are two popular variants of the main
links at the bottom of the page, which requiresassembly style of three modules in triangular
only 30 units.pyramids, both using the same flaps and pockets
Three interconnected Sonobe units will form anand compatible with it:
open-bottomed triangular pyramid with aJoining four modules together (instead of three),
right-angle apex (equivalent to the corner of aforming a flattened square pyramid that can
cube) and three tab/pocket flaps protruding frombecome part of a quilt or a larger polyhedral face,
the base. This particularly suits polyhedra thate.g. in 12 and 24 modules large cubes.
have equilateral triangular faces: Sonobe modulesJoining only two modules, forming a triangular fin
can replace each notional edge of the originalthat can be used as an ornament for suitable
deltahedron by the central diagonal fold of onemodels and to make a 1 module triangle (one fin,
unit and each equilateral triangle with a right-anglemade with the two halves of the same module)
pyramid consisting of one half each of three units,or a 2 module square (two fins).
without dangling flaps. The pyramids can be madeThe popularity of Sonobe modular Origami models
to point inwards; assembly is more difficult butderives from the simplicity of folding the modules,
some cases of encroaching can be obviouslythe sturdy and easy assembly, and the flexibility
prevented.of the system.
The simplest shape made of these pyramids,References
often called "Toshie's Jewel", named after origamiTakahama, Toshie, and Kunihiko Kasahara. Origami
enthusiast Toshie Takahama, is a three-unitfor the Connoisseur. Japan Publications, Tokyo,
hexahedron built around the notional scaffold of a1987.