Civic Membranes is an inventive re-imagining of downtown St. Louis Civic Center in the form of a public plaza and recreation complex. The program includes a restaurant, retail space, market, live performance theater, and fitness center. The block containing City Hall is revamped with a new paving strategy and an elegant translucent canopy which covers both enclosed and outdoor spaces. This canopy assembly features a tensile fabric attached to steel tube arches held in tension by a series of cables. The structural arches, some of which are enclosed by a light curtain wall system, form a dynamic series of spaces and celebrate the nearby iconic Gateway Arch. The Tensotherm fabric provides insulation and diffuses sunlight to create a stunning natural illumination. The material is also able to span great distances with a delicate minimal structure. The resulting ethereal tactility is ideal for public and recreational activities. The form and materials of the project are the result of comprehensive research on the mitochondrial membrane and how its mechanisms of density control and energy production can apply to the urban scale.