The double-layer DVD+R system uses
two thin embedded organic dye films for data storage separated by a
spacer layer (see figure). Heating with a focused laser beam
irreversibly modifies the physical and chemical structure of each layer
such that the modified areas have different optical properties to those
of their unmodified surroundings. This causes a variation in
reflectivity as the disc rotates to provide a read-out signal as with
commercially pressed read-only discs.