The design is based in a curve creased technique called Hot Gluing. Given two arbitrary 1 curvature surfaces, even if they have taper, its intersection will be foldable in two individual pieces as they share length of perimeter, given by its intersection.

Then I did the proper Zund layout and added some curved creases on the chest to provide stability and a clamping forze that make the helmet much more stable.

The fabrication were straight forward and it was so cool to see how the perimeter matches perfectly in two pieces with completely different curvature. But they a geometrical place on their perimeter!