(Addendum: If you're wondering what makes it more rigid than traditional X-shape extrusions, it's partly because the joints are well designed, but mostly becaus

(Addendum: If you're wondering what makes it more rigid than traditional X-shape extrusions, it's partly because the joints are well designed, but mostly because the torsional rigidity of a thin-walled section is proportional to the square of the enclosed loop area): https://ocw.mit.edu/courses/16-20-structural-mechanics-fall-2002/d01996bd6822461f4dcbdc3fbf2ea16f_unit12.pdf https://ocw.mit.edu/courses/16-20-structural-mechanics-fall-...