The technology used for reaction injection moulding polymers and polymer composites is very similar to the stopped-flow technique used for the measurement of very fast reaction rates. The major differences is that of scale and that a mould is used in the former in which the low viscosity polymer precursors react to produce a solid whereas with the conventional kinetic studies by stopped flow methods the reactants are feed into a spectrometer cell and the reaction followed with the reactants remaining in the liquid state. When the polymerisation chemistry is very fast relative to the rate at which reactants are delivered to the mould in reactive injection moulding (RIM) processes, the dynamics of the reagent delivery becomes convolved with mixing quality, the reaction rates rind the heat transfer rate characteristics of the mould. The quantification of the complex overall dynamics interactions is not possible without considering the RIM process to comprise distinctive elements, for example, the reagent delivery system, an impingement mixing device and a mould in which a fast non-isothermal reaction takes place to give a finished product. Some simplified aspects of the different modelling and simulation approaches which have been used in our own laboratories towards the understanding the overall process are outlined.