 Colloidal silica-dispersed UV-curable resins are used for the hard coating since, according to the Blu-ray Disc Association, they offer the best tradeoff between scratch-resistance, optical properties, and productivity.The Blu-ray Disc specification requires the testing of resistance to scratches by mechanical abrasion.In contrast, DVD media are not required to be scratch-resistant, but since development of the technology, some companies, such as Verbatim, implemented hard-coating for more expensive lines of recordable DVDs.