Rigid folded structures

Folding thin plates is 
another method to gain
structural performance 
without unduly increasing

weight. 
Isotropic thin materials, which are not elastic, cannot be bent along a folding edge (more general: along the generating lines of a cylinder or a cone). 
The principle of folding is ubiquitous in nature: 
leafs and insect wings, for instance, are folded for reasons of structural performance. The same principle is applied in architecture in folding structures. 
The largest application field for folding structures is in material structuring, e.g. paper,
sheet metal.