Bocce balls are usually made from a hard synthetic material, most commonly resin or poly-resin. Modern recreational bocce sets often use molded plastic because it is durable, weather-resistant, and inexpensive. Higher-quality sets may use a denser composite or thermoset resin to give the balls a more solid feel and better balance.
Traditionally, bocce balls were made from wood, stone, or metal, but those materials are less common today. Wooden balls were used in older versions of the game and are lighter and less uniform. Stone or metal balls were stronger but heavier and less practical for casual play.
In official or competitive bocce, the balls are generally made to exact size and weight standards, and the material is chosen to ensure consistent rolling, durability, and resistance to cracking. The surface is usually smooth or slightly textured, and the balls are often colored in contrasting patterns so players can distinguish teams easily.
The smaller target ball, called the pallino or jack, is typically made from plastic or another hard synthetic material as well.
So, in short, most bocce balls today are made of hard resin or plastic, while older versions were made of wood, stone, or metal.