Crease (fold and unfold)

A crease, or fold-and-unfold, is a fold that you make firmly and then open again so the line stays in the paper as a guide for later steps.

Fold as normal, press the line sharply, then open the paper back to where it was. Diagrams show this with a fold line and an arrow that goes out and comes back, or with a thin line indicating an existing crease. These guide lines are used later for alignment or for collapsing a base.

Weak creases are the main cause of trouble in later steps. Press each crease firmly with a fingernail along its full length. Also check that crease lines run exactly corner to corner or edge to edge, because small errors grow as the model develops.

How to fold a crease, step by step

1
Make the fold the diagram shows, valley or mountain, lining up the corners or edges exactly.
2
Press it flat and sharpen it with a fingernail along its whole length; this line will be used again later.
3
Unfold the paper back to its previous position.
4
Check that the new line runs exactly through the points the diagram names, such as two opposite corners.
5
If a later step will bend this line the other way, fold it in the opposite direction now as well. Folders call this pre-creasing in both directions.

Common mistakes and how to fix them

You can’t find the crease a few steps later
It was made too gently. Crease firmly with a fingernail, and hold the paper up to the light to check that the line is clear.
The crease misses the corner slightly
Small errors grow: a line that misses by a millimetre leaves a much bigger gap once the paper is collapsed. Refold along the same line rather than adding a second crease beside the first.
The sheet is covered in stray lines
Only crease where the diagram asks. In a collapse the paper folds along whichever line is easiest, so extra creases make bases fold the wrong way.

When you’ll use it

Creases are how origami measures without a ruler. Folding an edge to a crease halves a distance, and folding to the crossing of two creases finds a center. That is why so many diagrams begin with a few creases: the Masu Box creases both diagonals and then divides the square with more creases before a single wall stands up, and the Pinwheel divides its square into a four-by-four grid. Creases also store the shape of moves that come later. A reverse fold, a sink or a collapse goes smoothly only when the paper already knows where to bend, which is why pre-creasing is the most useful habit to build.

Practice it on these models

Advanced15 min · 19 steps

Paper Crane

The origami crane is the traditional Japanese orizuru, a bird with spread wings folded from a single square without cuts or glue. It is an advanced model: expect about 15 minutes for your first one, mostly spent learning the petal fold and inside reverse fold.

Easy5 min · 10 steps

Paper Boat

The origami paper boat is a classic folded from a rectangular sheet, passing through a paper hat on the way to a small boat that really floats. It is an easy model that most children and adults finish in about five minutes.

Easy5 min · 8 steps

Origami Heart

The origami heart is a flat, symmetrical heart shape folded from one square, ideal for slipping into a card or envelope. It is an easy model that takes around five minutes and uses only simple valley and mountain folds.

Intermediate8 min · 9 steps

Masu Box

The masu box is a traditional Japanese square box folded from a single sheet that locks together without glue. It is an intermediate model that takes about eight minutes, with one three-dimensional step where the walls are raised.

Crease: questions

Why do diagrams ask you to fold and then unfold?+

The crease becomes a guide: a line to fold an edge to, or a hinge that lets a base collapse neatly later. The preliminary base and the waterbomb base both collapse along creases made in advance.

How is a crease shown in a diagram?+

With a fold line and an arrow that goes out and comes back, meaning fold and unfold. Creases already in the paper are drawn as thin solid lines. Our guide to reading origami diagrams shows each symbol.