Back for seating unit

A compliant back comprising:

• a flexible shell having at least one top and at least one bottom connection vertically spaced from the at least one top connection, the bottom connections being in front of a bottom of the shell so that the bottom connections define an axis that is adapted to be generally aligned with a seated adult user's hip bone when the seated user's torso is against the shell, the shell having a stiff thoracic section, a stiff pelvic section, and a lumbar section, the lumbar section characteristically being noticeably flexible in a horizontal forward direction, such that the shell can be easily flexed to provide different shapes for optimal lumbar support, but the lumbar section being substantially incompressible in directions toward the thoracic and pelvic sections so that the lumbar section causes the thoracic and pelvic sections to pivot along predetermined paths about the top and bottom connections when the lumbar section is flexed, such that the compliant back undergoes controlled flexure between the top and bottom connections upon flexure of the lumbar section caused by flexure of a seated user's back.

A seating unit comprising:

• a back frame;
• and
• a back operably attached to the back frame at a top connection and operably attached to the back frame at bottom connections, the compliant back including a stiff thoracic portion and a stiff pelvic portion connected by a flexible lumbar portion, the bottom connections being forward of the pelvic portion, the top and bottom connections and thoracic, pelvic, and lumbar portions being constructed so that when a seated user flexes their lower back rearwardly, the pelvic portion of the back moves pivotally downwardly and rearwardly, the lumbar portion of the back flexibly moves generally rearwardly to form a more planar arrangement with the pelvic portion, and the thoracic portion of the back pivots about the top connection, whereby the back, in combination with the back frame and base assembly, is adapted to provide postural support for a seated user's back that is very comfortable and yet posturally supports significant flexing and moving of the seated user's torso and spine.