Paper for currency

Most banknotes are made from cotton paper (see also paper) with a weight of 80 to 90 grams per square meter. The cotton is sometimes mixed with linen, abaca, or other textile fibres. Generally, the paper used is different from ordinary paper: it is much more resilient, resists wear and tear (the average life of a banknote is two years), and also does not contain the usual agents that make ordinary paper glow slightly under ultraviolet light. Unlike most printing and writing paper, banknote paper is infused with polyvinyl alcohol or gelatin to give it extra strength. Early Chinese banknotes were printed on paper made of mulberry bark and this fiber is used in Japanese banknote paper today.

Most banknotes are made using the mould made process in which a watermark and thread is incorporated during the paper forming process. The thread is a simple looking security component found in most banknotes. It is however often rather complex in construction comprising fluorescent, magnetic, metallic and micro print elements. By combining it with watermarking technology the thread can be made to surface periodically on one side only. This is known as windowed thread and further increases the counterfeit resistance of the banknote paper. This process was invented by Portals, part of the De La Rue group in the UK. Other related methods include watermarking to reduce the number of corner folds by strengthening this part of the note, coatings to reduce the accumulation of dirt on the note, and plastic windows in the paper that make it very hard to copy.