They also have to be stored at some point on a physical carrier for later access. One factor that most, if not all documents, have in common is their reliance on polymeric materials. The traditional materials of paper, parchment, leather, palm leaves etc. are all natural polymers. The newer media of tapes, discs and films rely on man-made polymers such as PVC and polyester. The rate of chemical de-composition of the various polymers varies greatly.
All polymers decay.
The decay cannot be stopped - but it can be slowed down by careful handling and favourable storage. It can also be greatly accelerated by careless handling and poor storage. All the storage conditions given in standards and other publications are for guidance. If the conditions are met, the decay does not stop. The figures quoted for temperature and humidity levels are a compromise between the rate of decay on the one hand and the costs of maintaining the conditions, of transfer and of conservation on the other.