Collectible coins include a variety of types such as proof coins, which are specially made for collectors and feature a high-quality finish. In the United States, the 25-cent (quarter) coin is a frequently collected denomination. The 2017 Proof Set contains a selection of coins, including the quarters, produced using a special minting process that results in a mirror-like surface and sharp details, making them highly sought after by numismatists. These sets are often sold in protective packaging to preserve their condition and appeal to collectors.