http://en.wikipedia.org/wiki/Compact_Disc go to Physical details and it it is there
A CD is made from 1.2 millimetres (0.047 in) thick, polycarbonate plastic and weighs 15–20 grams.[22] From the center outward, components are: the center spindle hole (15 mm), the first-transition area (clamping ring), the clamping area (stacking ring), the second-transition area (mirror band), the program (data) area, and the rim. The inner program area occupies a radius from 25 to 58 mm.
A thin layer of aluminium or, more rarely, gold is applied to the surface making it reflective. The metal is protected by a film of lacquer normally spin coated directly on the reflective layer. The label is printed on the lacquer layer, usually by screen printing or offset printing.
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