PPy actuators have many features suitable for many cutting edge applications ranging from biomedical to micro/nano manipulation systems. In this paper, we first establish a mathematical model describing the voltage input, and bending displacement and force outputs of the PPy actuators, and then use the model to optimise/improve their shape. With reference to their operation principle, we draw an analogy between the thermal strain and the real strain in the PPy actuators due to the volume change to establish the mathematical model, which is a coupled structural/thermal model. The finite element method (FEM) is employed to solve the model. The propagation rate of the ion migration into the PPy layers is mimicked with a temperature distribution model. Theoretical and experimental results demonstrate that the model is effective in predicting the bending angle and bending moment outputs of the PPy actuators quite well for a range of input voltages. Further results are presented to demonstrate that the thicker is the root of the actuator, the higher are the bending angle and the bending moment.