Interiority is always based on something exterior, something with extension, something that cannot be internalized or appropriated. Things with extension are spatial. “Each contains within itself the condition, which make its opposite possible. A boundary with its own complex topography seems to appear between the two. It is not clearly delimited; it screens by interposing series of filters, or marks out subtle openings and partially uncovers inner spaces.” The confines of filtration and connection (from absolute individuality and intimacy to ultimate conformity) represent the interiority; Interiority is nothing other than exteriority.
Filtration gets the meaning when changing of the levels shows up, this is when centripetal forces lead to intimacy and centrifugal forces lead to conformity or extreme connectivity. Intimacy is profound interiority. “The intimate represents a between quality of space. If we shift the emphasis from the substantivizing of the intimate, its corporeality, to its condition of nexus or relationship, we discover another intimacy, which is based on our consideration of the intimate as one of the ways in which we relate to ourselves and to the world (exteriority).”
Sloterdijk explains his version of Foam City like this: “The co-isolated foam of a society conditioned to individualism is not simply an agglomeration of neighboring (partition-sharing) inert and massive bodies, but rather multiplicities of loosely touching cells of life-worlds.” That is to say, we always share at least one partition with an adjacent world cell, we are isolated, but not alone in our isolation, separated out, but also sharing in the behavior of this structural stuff that is foam, a behavior or expression that might not at first be read in the local encounter, but which becomes clearer the more encounters occur in a system. It means that we construct interiority in our isolation but this isolation has meaning when we have connection to exteriority. So we bring exteriority into our isolation and filter it by our constructed limitations, and create interiority that stands for subjectivity. This boundary- filtration / connection- can explain multi interiorities and multi exteriorities in architecture within the space-time.