Seat factors are characteristics of seats that influence people's postures. Seat factors such as lumbar prominence and seat pan stiffnesses were defined and measured for a variety of automotive seats. Seat factors such as these serve as a basis for evaluating and comparing seats. They were useful for selecting seats and designing experiments for human subject testing in the ASPECT program. Seat factors are also candidates for independent variables in statistical posture prediction models. The Seat factors described in this paper were measured with the current J826 manikin. They will be redefined for use with the new ASPECT manikin.