Alejandro Zaera-Polo’s describes the envelope as the most important element of his architecture because it links technology, representation and politics. The envelope is more than a surface, it establishes the relationship between the shape of the container and the construction of the skin. By categorizing building envelopes into four distinct typologies (Flat Horizontal, Spherical, Flat Vertical, Vertical) he explains their potentials, and presents projects in relation to each category.