The “Bubble” is an inflatable event space planned for the cylindrical courtyard of the Hirshhorn Museum. In respectful dialogue with this Modernist icon originally designed by Gordon Bunshaft in 1974, the Bubble is an architecture of air: a pneumatic structure enclosed only by a thin translucent membrane that squeezes into the void of the building and oozes out the top and beneath its mass. In contrast to the familiar strategy of roofing over courtyards of institutional buildings, the Bubble produces a soft building inside of a hard one in which existing and new spaces, both interior and exterior are playfully intertwined. The ephemeral structure is erected once a year for two months. The additional 11 000 sf of sheltered space accommodates audiences of 500–800 for an array of public events including performing arts, film, lectures and debates. Its form is shaped by a series of cable rings that constrict the membrane, pulling it away from the inner wall of the courtyard while other cables tether it into place. The resulting contours act acoustically and produce changing shafts and pockets of outdoor space experienced from the ground and the galleries on the second and third levels.