I recently wrote two tutorials on the basic concepts and the math behind designing crease patterns for pleated forms. Here I will talk about how to fold the form from the crease pattern, adapting the folding methods from the simpler forms to more complex designs. Here is the crease pattern I developed in my previous tutorials:
As far as paper choice, I find that heavier papers that wet-fold well work best for this style of folding. Elephant Hide paper is well-suited for these forms. I have also used Strathmore charcoal and pastel paper and Canson Mi-Teintes paper, but these papers are a bit more limited in their suitability. Other papers that work well for folding tessellations are probably going to work well for these forms too.
In general, the reference points for this type of model are extremely difficult to find by folding, and relatively small errors can make a big difference in the final shape. It is usually much easier to use a ruler to find the reference points for the ends of the straight folds and along the curved folds. I usually round the measurements to the nearest 0.5 mm or 1/32 inch. The straight valley folds are easiest to find first, and then the curved mountain folds can be filled in.
As with any crease pattern, the next step is to pre-crease along all the fold lines. For the straight folds, I typically score the folds with a scoring tool. This makes it much easier to make the folds look clean and neat, and it also speeds up the folding process.
For the curved folds, there are several approaches. One possibility is to score and then fold the curves. I sometimes cut a template from cardstock or another sturdy material to score those folds. This only requires a few reference marks on the paper and can make the curves more consistent. However, any imperfections in the template will be repeated in every gore. Also, any mistakes will be very difficult to fix because the scoring tool cuts into the paper.
Another approach is to fold the curves by hand. This generally requires measuring more reference points for each curve. Folding consistent curves is more challenging than folding straight lines, and folding the curves by hand is generally slower than using a template. However, especially for new designers, a big advantage of folding the curves by hand is that it is easier to tweak the curves as needed while collapsing the form and clean up any imperfections.
Once all the folds are pre-creased, the next step is to transform the paper from a flat sheet into a tube. Since there is one more gore than is needed to go around the form, the first and last gore will overlap. Glue the front of the gore on one end of the paper to the back of the gore on the opposite end.
Often, the pre-creases need to be reinforced at this stage. For each mountain-valley crease pair, fold both creases and pinch along the folds. This makes it easier to collapse the final shape.
To collapse the form, I find it easiest to start with the base. This will use the mountain and valley folds that are already pre-creased. Squeeze the paper together using the pre-creased folds, and push down on the base to collapse it. It can take a little practice to collapse the base smoothly. Using tape to help hold the folds in place can make the collapse easier, and sometimes wet-folding is needed to get the base to stay in place.
Then, collapse the rest of the form along the pre-creased mountain and valley folds. Typically, wet-folding is required to lock the curves in place. While the paper is drying, either tape or clips can help hold the shape in place as needed. Each of these approaches brings its own advantages and disadvantages. Sometimes clips can dent the paper, and tape can tear the paper, especially if it is removed before the paper is completely dry. If the wet-folding does not hold the paper in place well enough, a small amount of glue will often help.
The finished form from the design looks like this, not too far from the original design: