A seat portion (14) for a seat (10) wherein the seat portion (14) includes a panel having a rear portion to support the occupant. The rear portion has a longitudinal centerline and incorporates two zones (162) on either side of the longitudinal centerline. Each of the zones has a first pattern of weakeners arranged in a series of spaced sinuous lines. Furthermore, a substantial portion of the panel, apart from the zones (162) may also be provided with a pattern of weakeners arranged in a series of spaced sinuous lines (163), interrupted by the zones (162).