This book gives a fresh point of view on the curing processes, structure and properties of crosslinked polymers. The general view is that the structure and properties of crosslinked polymers are defined by their density, this book demonstrates that the parameters are defined by the supermolecular (a more precisely, supersegmental structure) of the crosslinked polymers. The quantitative relationships of the structures/properties are obtained for these polymers. Using an epoxy polymer as a nanofiller for a nanocomposite is discussed and a new class of polymer is proposed. The introduction of the nanofiller gives variation in the mechanical properties, degree of crystallinity, gas permeability and so on. The use of these crosslinked polymers as natural nanocomposites is proposed. Practical methods of crosslinked polymer's supersegmental structure regulation are considered, and all the changes that this gives their properties are detailed. This book will be of significance to all material scientists and students of material science.