This essay examines two materials found on the walls of a British psychiatric hospital: shatter-proof glass and steel-reinforced concrete. Interested in their constitution through and of the institutional space, it explores these common building materials’ capacities to tolerate as well as to hold and contain. In doing so, the essay contemplates visually and textually where institutional space and practices begin and are bounded. The authors’ own voices enter in an epilogue, reflecting on their role in facilitating and testing the tolerance of institutional spaces. In doing so, they point towards architectural features in which these walls and their particular forms of boundaries between the inside and the outside of the psychiatric institution are constitutive of spaces of tolerance: they contain and regulate the users of the spaces (staff, patients, visitors as well as researchers). The tolerance articulates as selective yielding and holding. © 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.