Carbonless papers are bond papers which are been chemically coated to react when pressure is applied (from a pen, output printer, etc.) One coating, CB (coated back) consists of microcapsules containing colourforming dyes. Under pressure, these capsules rupture, releasing the dyes which are then absorbed by the second sheet, CFB (coated front and back). This pressure causes the following sheets to react in the same way until the last sheet CF (coated font) reached.
Carbonless papers are used for books or pads where multiple copies are required, eg invoice books, order books, application forms etc.