Foundational folds

The two creases everything starts from

A valley fold brings the paper toward you so the crease sinks away like a valley. A mountain fold folds the paper behind so the crease rises toward you. Diagrams draw a valley as a dashed line and a mountain as a dash-dot line, and nearly every other instruction is some combination of the two.

Precreasing

Precreasing means folding and unfolding to leave a crease without keeping the fold. Complex models often ask you to precrease a whole grid first, then collapse the flat sheet along those lines at once. It feels slow at first and saves trouble later, because the paper already knows where to go.

The four classic bases

A base is a repeatable folded shape that many models begin from. Four are worth knowing well:

• Kite base — two adjacent edges folded to a centre line. The simplest, and the start of many animals.
• Fish base — built from the kite, adding two points; the start of fish and some birds.
• Bird base — four points from a square; the foundation of the crane and many flapping birds.
• Frog base — the most layered of the four, yielding many points; used for flowers and frogs.

The bird and frog bases both grow out of a preliminary square base, so practising that single collapse pays off twice.

Reverse folds

Reverse folds change the direction of a flap and are the step beginners most often stumble on. There are two:

1. Inside reverse fold — the point is pushed inward between its layers, often used to make a head or a bend.
2. Outside reverse fold — the point is wrapped around the outside of its layers, used for beaks and feet.

Both are far easier if you precrease the fold line first in both directions, so the paper hinges willingly rather than fighting you.

A base-to-model map

Reading a sequence

Further reading: Yoshizawa–Randlett system (Wikipedia)