The third book in the series from Columbia University is focused on metals. Metals, as surface or structure—as the generators of space—play a role in nearly every strain of modernization in architecture. They define complete geographies of work, production, and political life. Non-architectural metals delivered in automobiles, and hard goods in the United States and worldwide have all been sourced as the engines of the sprawling late twentieth-century city in all of its forms. But in the received aspects of architectural history, metals, and in particular steel, remain less diluted; they are presented as intrinsic to the profession as material precedes concepts—they are carriers of architectural meaning. Few concepts are as central in structural engineering as the ability of a material to sustain plastic deformation under tensile stress—the standardization of historically known deformation limits or ductile properties in most materials allows architects and engineers to keep the analysis of structure within known parameters of finite element analysis rather then materials science. If the goal is avoid fracture, the boundaries are set and the limits of ductility are observed. Post Ductility refers to the literal aspects of material behavior—in this case of metals—but also of aspects of architectural and urban space that are measured by less verifiable but nonetheless real quotients of stress and strain. It is the tension and compression of space that gives form or coherence to form. In either the case of engineering and architecture, formerly daunting degrees of risk seem to have been diminished; new levels of sophistication in calculation lower the risk tolerance for fracture, while more metaphoric readings of limits in architectural and urban space seem to have been long surpassed, at times with abandon. The counter-effort has been quite strong if not successful: there are those that want to recreate dense cities by means of compression and there are immense forces of spatial extension by way of economics, communication and transit. Space is pulled to elastic limits and made thin—as highly malleable materials such as gold or lead—as it is also often re-compressed as forms of urban density. If metals are a significant origin for architecture and indeed whole cities - from buildings to automobiles and labor, then what are the limits or equations that offer a new evaluation of both metals, but also of material in a wider sense, as a determining component of the built world? What does an engineer and architect bring to this arena in both local and global circumstances?