The theory of modulus tailoring is mainly used in matrix-fibril type of bicomponent fibers. Classification based on the relative moduli of the two components depends to a great extent on the properties and use of the blends. For example, adding of a disperse phase of higher modulus generally increases the overall modulus and is frequently used to reduce the creep of elastomers. In contrast, adding of a low modulus polymer in the blend is generally used to improve the impact resistance and elongation-to-break of rigid plastics.