Abstract: A foam chair cushion having transverse support ribs is provided for reduction of shear stress between a person's skin and the surface of the chair cushion. The chair cushion may include transverse, lateral support ribs upon the support surface of the cushion. The support ribs have a predetermined cross-sectional geometry that is curvilinear, with a superior aspect generally disposed for receipt of a person and a inferior aspect opposite. The inferior aspect of the cross-section of the support ribs may undercut the portion of the support ribs vertically above it. Having such cross-sectional geometry, the support ribs are directionally oriented, either toward the one end or the other of the chair cushion. The chair cushion may include support ribs that are directionally oriented toward the foot of the chair in regions adapted for the person's upper torso, buttocks, and lower legs, and directionally oriented toward the head of the chair in a region adapted for the person's thighs.