Commercial cork is the outer bark of the cork oak (Quercus suber) grown in the western Mediterranean. The first layer is commercially useless; thus, it is removed from the tree and discarded when the tree is approximately ten years old. When the tree is twenty to twenty-five years old and has a diameter of approximately 15.75 inches (40 centimeters), a usable cork layer 1.2 to 3.9 inches (3–10 centimeters) thick can be harvested. A similar layer can be harvested approximately once every ten years until the tree is approximately 150 years old.

The cork of a cork oak breaks away at the cork cambium and can be peeled off without harming the tree. Cork consists of densely packed cells (about one million cells per cubic centimeter) that contain the plant wax suberin, making cork impermeable to liquids and gases. Half of its volume is trapped air; therefore, it is four times lighter than water. It is virtually indestructible, fire-resistant, and durable; resists friction; and absorbs vibration and sound.