(Non)existence of Pleated Folds: How Paper Folds Between Creases

TL;DR

This paper proves that certain classical origami models cannot be folded with standard crease patterns in the mathematical zero-thickness paper model, but can be folded with additional creases, revealing new structural insights into paper folding behavior.

Contribution

The authors introduce a new structural theorem characterizing uncreased flat surfaces, advancing understanding of the geometric constraints in origami folding models.

Findings

Pleated hyperbolic paraboloid cannot be folded with standard creases in the zero-thickness model.

Additional creases enable folding of the hyperbolic paraboloid, suggesting real paper folds differently.

Straight creases must remain polygonal after folding.

Abstract

We prove that the pleated hyperbolic paraboloid, a familiar origami model known since 1927, in fact cannot be folded with the standard crease pattern in the standard mathematical model of zero-thickness paper. In contrast, we show that the model can be folded with additional creases, suggesting that real paper "folds" into this model via small such creases. We conjecture that the circular version of this model, consisting simply of concentric circular creases, also folds without extra creases. At the heart of our results is a new structural theorem characterizing uncreased intrinsically flat surfaces--the portions of paper between the creases. Differential geometry has much to say about the local behavior of such surfaces when they are sufficiently smooth, e.g., that they are torsal ruled. But this classic result is simply false in the context of the whole surface. Our structural characterization tells the whole story, and even applies to surfaces with discontinuities in the second derivative. We use our theorem to prove fundamental properties about how paper folds, for example, that straight creases on the piece of paper must remain piecewise-straight (polygonal) by folding.