This book provides another approach for the replacement of glass and other inorganic fibers as reinforcement for polymer composites. Although this approach does not have the advantages of biodegradable natural fibers, the synthetic polymer-polymer composites are more environmentally acceptable than glass fiber reinforced composites because of their organic nature.In addition to their environmental advantages, as compared to the polymer composites with mineral reinforcement with high loading rates, they have mechanical properties that allow manufacturing light-weight products and constructions; an importance in transportation vehicles and aircrafts.