Abstract: A chair includes a base, a backrest and a back brace supporting the backrest from the base. The base may include a seat assembly made up of a pan and a flexible support membrane over an upward opening cavity defined by the pan. The back brace may provide a flexible support for the generally planar member formed as a serpentine shape defined by a first curved portion opening toward said base and a second curved portion opening away from said base. The backrest may have an outer frame made from an extruded member having a generally tubular member and a fin coextruded with said generally tubular member to provide a fastening substrate for panels. The base may further include a leg assembly made up of a plurality of leg members and a joiner member joining horizontal portions of the leg members.