Book excerpt: Some time ago, Walter Benjamin and Asja Lacis used the term "porosity" with reference to Naples’ urban characteristics – spaces merging into each other and providing the backdrop for the unforeseen – improvisation as a way of life. Today, the term "porosity" in this context is increasingly used conceptually. Well-known authors from the worlds of architecture, town planning, and landscape design embark on a search for new concepts for a life-enhancing, user-friendly city – with reference to this enigmatic term. The term refers to the overlaying and interweaving of spaces and structures, to urban textures and their architectural properties and qualities – to cities with radically mixed urban functions.