 Similar to CD-RW and DVD-RW, a phase transition alloy (often GeSbTe or InAgTeSb, Copper silicate (CuSi) or other alloys can also be used, like Verbatim's proprietary MABL) is used for BD-RE discs.Melting the material with a very high power beam turns it into an amorphous state with low reflectivity, while heating at a lower power erases it back to a crystalline state with high reflectivity.In BD-RE discs, the data layers are surrounded by a pair of dielectric Zinc Sulfur-Silicon Dioxide layers.