A head-pan diaphragm structure attachable to or an integral part of a seat back structure, the head-pan diaphragm structure including high-performance fibers and the head-pan diaphragm structure positionable in a head strike target area of the seat back structure. A seat back assembly including a seat back frame member including spaced portions, a torsion bar attached between the spaced portions, a head-pan diaphragm structure positioned in a framed opening formed by the torsion bar and a portion of the seat back frame member, the head-pan diaphragm structure positioned in a head strike target area, and the head-pan diaphragm member including integrated high-performance fibers.