The world is facing a shortage of key metals used in manufacturing. Two of these are zinc and copper. The U.S. Mint estimates that there are more than 200 billion pennies in circulation. Each contains 2.4375 g of zinc and 0.0625 g of copper. That's nearly 500,000 metric tons of zinc and more than 100,000 metric tons of copper sitting in empty peanut butter jars and plastic trays next to the cash register, doing nothing.
Meanwhile, a dollar bill stays in circulation only 12 to 18 months, while coins last for decades before they must be replaced. In 1862, when the U.S. first adopted paper currency, the lowest value deemed worthy of a banknote was $1 -- worth $23 today. The burden of routine use is supposed to fall on durable coins. Flimsy bills were never meant for everyday spending.