Abstract: A one-piece seat frame structure having a plurality of parallel curvilinear slots which demarcate cantilever-action spring segments. A thin-walled, hollow, molded plastic body, or a similar body of another suitable relatively rigid material having resilient characteristics, has a pair of side walls, a rear wall, a front wall and a positively bowed top. A plurality of parallel curvilinear slots are provided through the top to demarcate a plurality of parallel curvilinear spring segments. In response to a typical load created by a seat occupant, the spring segments are deflected downward in a cantilever manner.