Valley & Mountain folds

The most basic origami technique is the valley fold. This is the type of fold that everyone does, whether or not they realise it. In origami, we often fold one edge to meet another edge, as shown here.

The arrow in the first image indicates we’re taking the lower edge to the opposite edge. In other words, folding in half. The second image shows the result. The diagram may indicate the position of the paper relative to the previous diagram, or not.

It’s equally possible that you fold an edge to meet a crease, or an intersection of creases. The exact location may be obvious and not precisely indicated, or it may be indicated with small dots or circles. Here, it’s fairly clear that the corner folds to meet the centre.

Here, the target point is just above the centre, so it is indicated with small dots at the start and end of the arrow. There may sometimes just be one dot at the target end.

Most origami diagrams show an overhead view, like a 2D architects plan. If you’re lucky, the artist will take the trouble to add extra edges to show the different layers, as above. If you’re really lucky, you’ll get 3D perspective, with an intermediate step showing the fold in progress, like this..

Whilst many valley folds are left in place, we can also do a “fold and unfold” – we make the valley fold, then unfold the paper to leave the crease. This technique is called making a pre-crease, since we don’t actually use the crease until later (at which point it may be more difficult to put the crease in accurately).

Here is the most common way of showing fold-unfold. The arrowhead shows that we take the lower edge to the opposite edge, make a crease, then unfold. Here is another way of showing the same fold. This time, the diagrams leave it up to the folder to decide which edge to fold to which, although the result is the same. Here is the result in both cases, a thin line, which indicates an existing crease. As the fold progresses, some of the less important creases may not be shown.

Arrowheads for valley folds may be solid, with curvy or straight edges, or even straight lines, or somewhere in between. Mountain fold arrowheads are different, as shown below.

A mountain fold is the opposite of a valley fold – the paper folds to the opposite side. This means you either have to hold the paper in the air to allow paper to fold underneath, or simply turn the paper over and treat it as a valley fold. This is usually easier. It’s also best to fold the paper away from your body rather than towards it.

The diagrams may not always show the valley fold being made this way, because the diagrams represent a pictorial story and the individual drawings don’t usually rotate from step to step. Turn the paper to whatever angle makes the fold easiest, then turn it back to match the next step in the drawings.

The empty half-arrow indicates a mountain crease and it shows the upper edge folding underneath. This is the result. A small section of the lower layer is shown, coloured white.

Here is the same move, shown in 3D and with an intermediate step. Note that the arrowhead, shown above disappearing behind the edge, can be fully seen. It has exactly the same meaning.

Naturally, we can have a “mountain fold and unfold”, where we make the mountain crease, then unfold the paper again. The arrowhead goes under the paper and can then be seen returning. We do this if this crease is used later and needs to be a mountain crease to make the folding easier.

Finally in this section, we can combine valley and mountain creases to form a pleat. These creases are usually put in one at a time, unfolded, then combined.

The paper has been precreased into quarters, then we’re instructed to make a pleat. This is the result shown in 3D, which helps us to see where the layers are. You may be unlucky enough to be given a 2D drawing, showing a directly overhead view.