Most pop-up models are built around a basic shape.
The shapes are constructed using variations and combinations of pop-up’s two major “building blocks” - the V-Fold and the Parallel Fold.
The same three rules apply to both types of mechanism:-
Every pop-up must span a gully.
The first gully is the spine fold down the middle of the base card.
Pop-ups must be “balanced” - or match - on each side of the gully.
With V-Folds the angles on each side must balance. (A + B = A + B)
With Parallel Folds the lengths must balance. (A + B = A + B)
Every pop-up creates new gullies
Additional pop-ups can be built onto these new gullies.