This paper describes an investigation into the key factors which contribute to an effective mode stirrer. The work concentrates on the lower frequency range, since all stirrers have poorer performance at low frequencies. The stirrer's shapes and sizes have been investigated, together with an optimization of the finer details in the stirrer's shape. The modeling of the mode stirred chamber has been performed using the transmission-line matrix (TLM) method. Software has been developed which, for each position of the rotating stirrer, builds the shape of the stirrer using thin, perfectly conducting boundaries. Results indicate that the design of the stirrer's basic shape has a small but significant impact on its performance. A genetic algorithm has been used to optimize certain parameters in the shape of the stirrer, and a fitness factor based on a free space model of the stirrer has been used. The free space model runs 1500 times faster than the model in the chamber. The optimization is shown to improve the stirrer's performance in three different sizes of chamber. Computer modeling has been verified by measurements performed in the chamber at the University of York.