Co-rotating twin-screw extruders are the prime process method to melt mix thermoset powder coating raw materials. The geometry of the extruder’s shear paddle is variable and not only determines the degree of shear, but also residence time distribution (RTD). These parameters need to be optimised in order to ensure adequate mixing, but without overlong residence within the heated barrel. The latter is of particular significance due to a growing trend within the industry towards low cure, temperature sensitive products. A method based on the use of flow analysis network (FAN) to determine pressure profiles, has been developed to estimate melt zone RTD. Simulations based on predicted flows and probability theory, compare well with results obtained from experiments in which a coloured marker pigment was added to the input raw materials.