What's Going On Folding the paper as if to make a paper fan makes a corrugated roadway. The folds form a series of triangles. Triangles form the strongest structures. A structure is anything that supports its own weight against gravity, plus the weight of another object. Compression is a push down on the structure that must be channeled to the ground.
Tension is a pull that stretches the structure.
Triangles support both of these forces. Compression pushes down equally on two sides of the triangle, causing the base to be pulled equally in two directions, which creates tension. The triangle is the strongest structure because all three sides bear the load. In a square, only two sides of the four bear the load. This equaling of the forces makes the triangle the strongest structure.