Because a CD's reflective metal layer and data layer are both directly beneath the thin lacquer surface of the label, data can be destroyed by even a small scratch on the top of a CD. The instrument used to label CDs should be seriously considered. Pens or markers with hard tips, or with solvents that can affect the protective layers, can scratch or damage the data layer; water-based felt-tip pens are safest. The data layer of a double-sided DVD is in the middle of the disc, surrounded by the substrate on both sides so scratches to either side are equivalent.