Pureland folding allows only simple valley and mountain folds. Since a pleat can be folded by first making a valley and then a mountain,
every piece that uses only a sequence of pleats, however complicated, belongs to pureland origami.
This gallery indicates some directions for pleat-based folding that incorporates more complex steps.

The first two pieces here are based on layering multiple second-order pleats to create loose paper.
The second two use twists in order to reverse parts of each pleat and create new layer and tension patterns.
The first technique has been used by several other folders to create boxes, crosses and other types of mostly regular protrusions.
It has also been used for a long time in box-pleated models such as Momotani's Steam engine.

Medium: elephant-hide; unryu.