Today, a large variety of plastics exists in archives, used mainly as data carriers, but also as toners in copiers, parts of machines, material for storage and preservation, etc. These materials are by no means uniform, but contain fillers, plasticizers, coatings, etc. To complicate the situation even more, the formulas of these materials are constantly changing. The various plastics and their ingredients that may be found in archives are discussed together with the diverse forms of degradation. A general means to counter degradation is appropriate storage. Machine-readable data are stored nearly exclusively on plastics. Preserving them requires periodic copying.