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Sink fold

A sink fold is a move where a point or corner is pushed inward into the model, reversing its creases so the point disappears inside instead of being folded over.

Crease the fold line firmly in both directions first. Then open the layers slightly, push the tip of the point into the model along the crease, and let the surrounding paper reverse around it before flattening. In an open sink the paper can be spread flat while you rearrange it; in a closed sink it cannot be opened, which makes it one of the harder moves in origami.

Sinks go wrong when the pre-crease is weak or when you push before the layers are free to move. Make the crease sharply, open the model as far as it will go, and ease the paper in rather than pressing hard. Diagrams show a sink with a mountain line across the point and a hollow push arrow. It is an intermediate to advanced technique not needed for any model on this site yet.

How to fold a sink fold, step by step

  1. 1

    Fold the point down along the line where it should sink, crease very firmly and unfold.

  2. 2

    Fold it the other way along the same line and unfold again.

  3. 3

    Open the model as far as the layers allow, so the creases around the point are free to move.

  4. 4

    Push the tip of the point down into the model along the crease; the creases around it reverse as it goes in.

  5. 5

    Ease the surrounding paper back into place so the sunk area lies flat.

  6. 6

    Close the model and flatten it.

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Common mistakes and how to fix them

  • The paper crumples instead of sinking

    The pre-crease is too weak or the model is not open enough. Re-crease sharply and open the layers further before pushing.

  • Only part of the point sinks

    Every layer of the point must reverse together. Push evenly from the tip, not from one side.

  • A closed sink seems impossible

    In a closed sink the paper cannot be opened flat, so the layers have to be coaxed inside a little at a time. Practice open sinks first.

When you’ll use it

Sink folds appear in intermediate and complex models, where they blunt a point, hide a corner or create a hollow without adding a new flap on the outside. A common use is to make a pocket for another flap to slide into, or to shape the top of a box or a head. If a diagram asks for a closed sink and it feels impossible, that is normal: even experienced folders take a few attempts. Fold that step slowly, with the model opened as wide as it will go, and re-crease the lines around the point whenever the paper starts to resist.

Sink fold: questions

What is the difference between an open and a closed sink?+

In an open sink the paper can be spread flat while you rearrange it, so you can see and control the move. In a closed sink it cannot be opened, and the paper must be pushed in blind; it is one of the hardest moves in origami.

How is a sink fold shown in diagrams?+

With a mountain line across the point and a hollow push arrow, the same arrow used for pushing paper in. The guide to reading origami diagrams shows the push symbol.

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