Why There Are Only Five
At each corner of a solid, at least three faces must meet, and their angles must add up to less than a full turn, or the corner would lie flat. With equilateral triangles, three, four or five can meet; with squares, only three; with regular pentagons, three again. Three hexagons already make a full turn, so no other combination works.
From First Model to Last
The cube and the tetrahedron fold up with few faces and are good first models. The octahedron and the icosahedron need more care, since four or five triangles meet at each corner. The dodecahedron, with its twelve pentagons, closes into a rounded shape that is very satisfying to finish.
Plato and the Elements
The solids take their name from the Greek philosopher Plato, who, in his dialogue Timaeus, matched four of them with the elements: the tetrahedron with fire, the cube with earth, the octahedron with air and the icosahedron with water. The dodecahedron he linked with the heavens as a whole.