* Pre-1982 Pennies: Made of 95% copper and 5% zinc, these pennies are almost entirely copper, a dense metal.

* Post-1982 Pennies: Made of a zinc core with a thin copper plating, these pennies have a lower density than the older copper pennies.

The difference in density is noticeable if you hold both types of pennies. The older copper pennies feel heavier and more substantial than the newer zinc core pennies.