A clamshell is formed when a single layer of blister packaging is folded over on itself, creating a hinge in the middle. An item or loose items are placed in the cavity, and the sides of the plastic fit together to close the package. Clamshell packages can be stock, or they can be custom-designed to fit a product perfectly. The closure is often heat sealed, or it can be left unsealed so that the package closes again after opening. Items commonly displayed in clamshell packaging are carpentry items, electronics, and foods.