A valley fold is the most fundamental fold in origami. You fold the paper toward you so the crease forms a “V” shape, like a valley between two hills. If you’ve ever folded a paper airplane or a greeting card in half, you’ve already made a valley fold.
How a Valley Fold Works
To make a valley fold, bring the edge of the paper up and toward you, folding it on top of itself. The crease line becomes the lowest point of the fold, sitting below the two layers of paper that rise on either side of it. Think of looking down into a shallow valley from above: that’s the shape your paper makes at the crease.
The key detail is direction. You always fold the paper toward yourself, so the flap lands on the near side. This is what distinguishes it from its counterpart, the mountain fold, where the paper folds away from you and the flap tucks behind. The British Origami Society puts it simply: a mountain fold is the opposite of a valley fold, with the paper folding to the opposite side. Every valley fold becomes a mountain fold if you flip the paper over, which is why the two are really just different perspectives on the same crease.
Reading Valley Folds in Diagrams
Origami diagrams use a universal set of symbols so folders worldwide can follow the same instructions regardless of language. A valley fold is represented by a dashed line along the crease, paired with an arrow showing where the paper moves. The arrow typically has a solid, filled arrowhead pointing in the direction you’ll fold. Arrowhead styles vary slightly between diagram artists (some use curvy edges, others use straight lines), but a solid arrowhead with a dashed line consistently means “valley fold.”
Mountain folds, by contrast, use a dot-dash line (alternating dots and dashes) and an arrow with an open, unfilled half-arrowhead. That empty arrowhead tells you the paper’s upper edge folds underneath, away from you. Once you can tell these two line types apart at a glance, you can read nearly any origami diagram, since valley and mountain folds account for the vast majority of steps in most models.
Valley Fold vs. Mountain Fold
The practical difference comes down to one question: which way does the paper go? With a valley fold, the paper comes toward you. With a mountain fold, it goes away from you. The finished crease looks identical on the paper itself. What changes is which side of the paper ends up on top.
In simple models like a paper cup or a basic boat, you’ll mostly use valley folds. More complex designs mix both types constantly, sometimes within a single step. At any point where multiple creases meet in a flat-foldable design, the number of mountain folds and valley folds is always related by a simple rule: the difference between them is exactly two. So if a point has five valley creases, it will have either three or seven mountain creases. This constraint, known in origami mathematics as Maekawa’s Theorem, is one reason complex origami patterns can be analyzed and designed with precision.
Tips for Clean Valley Folds
A sloppy valley fold early in a model compounds into bigger alignment problems later. A few habits make a noticeable difference:
- Work on a flat, hard surface. Folding in your lap or on a soft surface introduces slight curves. A table or desk gives you the resistance you need for a straight crease.
- Align edges before creasing. Line up the corners or edges that should meet, hold them in place with one hand, and only then press the fold flat with the other. Trying to fold and align at the same time leads to crooked results.
- Crease firmly and evenly. Run your fingernail or the back of a spoon along the fold with consistent pressure from one end to the other. A bone folder (a smooth, flat tool used in bookbinding and paper crafts) works even better for getting a razor-sharp line.
- Keep pressure consistent. Pressing harder in the middle than at the edges creates an uneven crease that can warp later folds.
Paper choice matters too. Standard origami paper (thin, square, colored on one side) is designed to hold a valley fold crisply. Thicker paper like cardstock resists folding and doesn’t hold creases as well. Printer paper works fine for practice but tends to be slightly slippery, so take extra care aligning edges before you commit to the crease.
Where Valley Folds Appear
Nearly every origami model starts with valley folds. The classic first step of folding a square in half diagonally is a valley fold. So is each triangular fold in a fortune teller, each wing crease in a paper crane, and most of the steps in a jumping frog. Even highly advanced models with hundreds of steps rely on sequences of valley and mountain folds as their core vocabulary.
Beyond traditional origami, valley folds show up in packaging design, pop-up cards, and engineering applications like deployable solar panels and airbag packing. The geometry stays the same whether you’re folding a paper hat or designing a structure that needs to collapse flat and expand later. Mastering the valley fold isn’t just the first step in origami. It’s the foundation for understanding how flat materials become three-dimensional shapes.