As money is handled over the course of months and years, it begins to break down. Folds eventually become small tears, which turn into bigger tears. Eventually, the money can no longer remain in circulation. Countries have begun replacing traditional paper bills with polymer banknotes made from a durable plastic. Polymer banknotes are advantageous for a number of reasons, but they have their faults as well.
Sticky When Wet
Polymer notes feel more like plastic than paper, which can cause problems in the event the bills get wet. When these notes come in contact with water or some other liquid, they tend to get stuck together, making them difficult to pull apart. This can be an annoyance for people who are trying to make a payment with wet bills, and could potentially lead to a purchaser handing a retailer two bills stuck together instead of one. Bank tellers may find this problematic as well, since sticky bills can be more difficult to count by hand.
Hard to Fold
You can fold paper money and place it in your pocket without a problem. The same can't be said for polymer money, which is designed specifically to resist attempts at folding. The use of polymer is intended to increase the life of a bill, but without being able to fold it at all, those who use folding wallets or prefer to carry bills in their pocket will have a difficult time making do. When a polymer banknote is folded, the action creates a crease in the middle of the bill. While paper notes fold back without much problem, the crease in the polymer bill remains there permanently.
Difficult to Sort
Money sorting machines in banks, casinos and other cash-intensive businesses are built to handle paper banknotes, and they do so with relative ease. The polymer banknote design is a different texture, one which is foreign to traditional sorting machines. The strength of the polymer material could potentially be enough to cause sorting machines to malfunction, since they are not designed to deal with bills of a different material. Having the machines altered to conform to new currency can be costly. Having them replaced outright would be even more of a financial hit.