Nitrile rubbers, both common and hydrogenated, revealed some kind of ordering, as detected by WAXS. Strain-induced crystallization is responsible for the enhanced degree of crystallinity for HNBR. In the case of NBR, another mechanism has been proposed, namely specific interactions between carbon-carbon double bonds from butadiene and cyano groups from acrylonitrile monomer units, leading to an EDA complex formation. Iodination reduces the degree of crystallinity of both materials; however, their stiffness increases as the result of modification, probably due to dipole-dipole interactions or hindering effects accompanying introduction of 'large" iodine atoms into the macromolecular structure.