Today, designing of machines and dies is done to a large extent with the help of computer programs. However, the predictions of theses programs do not always agree with the practical results, so that there is a need to improve the underlying mathematical models. Therefore, knowledge of the formulas, on which the models are based and the limits of their applicability is necessary if one wants to develop a new program or improve one already in use. Often the plastics engineer has to deal with different fields of engineering. The search for the appropriate equations in the various fields concerned can be time-consuming. A collection of formulas from the relevant fields and their applications, as given in this book, make it easier to write one's own program or to make changes in an existing program to obtain a better fit with the experiments. It is often the case that different equations are given in the literature on plastics technology for one and the same target quantity. The practicing engineer is sometimes at a loss judging the validity of the equations he encounters in the literature. During his long years of activity as an R&D engineer in the polymer field at the BASF AG and other companies, Natti Rao tested many formulas published while solving practical problems. This book presents a summary of the important formulas and their applications, which Natti Rao, in cooperation with the well-known resin and machine manufacturers, successfully applied to solve design and processing problems.