These days, urban buildings are playing just one penny-whistle tune: glass, glass, glass. It’s as if there were a material shortage and we had run out of everything else. I don’t miss exposed concrete, but what about limestone and brick, terra cotta and granite? But no, architecture has been reduced to one material—even spandrels and soffits are glass. What explains this phenomenon? Well, of course it’s cheap. The engineer figures out the structure, and the architect wraps it in a glass skin. And the helpful glass manufacturers work out the details for you. It’s also easier to design. No more worrying about junctions between materials, no more textures or finishes, no more colors, no more studying shadowing effects. Just wrap it up and it’s ready to go. Nor do you have to worry about energy—all-glass buildings are as green as you want. Houston, Boston, London, Dubai—it doesn’t matter. It used to be that cities had distinctive architectural characters, derived from different materials, different climates, different tastes. No more. It’s just all glass, all the time.