This paper reports on different parameters that influence the closed mould resin transfer moulding (CM-RTM) process for fiber-reinforced plastics. A sensitivity study of selective parameters is performed. This includes material parameters (i.e., viscosity, permeability), process parameters (i.e., temperature) and geometrical parameters (i.e., position of preform in the tool). Furthermore, fiber type and targeted fiber volume content are considered to validate the full range of fiber-reinforced plastics. As an example for the sensitivity study, the aeronautical carbon fabric G0926 and epoxy resin system RTM6 (both manufactured by Hexcel) are analyzed for targeted fiber volume contents in a range of ~60%. The infiltration of a rectangular panel was simulated with the flow simulation software RTM-Worx by Polyworx. It was found that the infiltration of a simple geometry can differ by app. Factor 3 in terms of duration, when only considering the tolerances of material and process parameters (“upper tolerance limit” vs. “lower tolerance limit” scenario). For different types of composite materials observed in this study, it can even go up to Factor 1,000. To achieve a reliable RTM process, these aspects—material types and range of tolerance—have to be considered.