A clamshell is a one-piece container consisting of two halves joined by a hinge area which allows the structure to come together to close. Clamshells are often made of shaped plastic material, in a way that is similar to a blister pack. The name of the clamshell is taken from the shell of a clam, which it resembles both in form and function.
Clamshell containers can be made of a variety of plastics such as polystyrene, polyester, PVC, foam sheets, etc. The material can be made by thermoforming or can be injection molded into the desired shapes. A single piece of material is used for the top and bottom with a "living hinge" that is integral to the material, rather than added separately.
Clamshells can use a variety of means of closing or sealing. Some have self-locking tabs, snaps, or have a friction fit. Others use adhesive, pressure-sensitive tape, labels, staples, or are heat-sealed.
When plastic clamshell containers are securely heat sealed, they are tamper resistant and deter package pilferage. These security packages are intentionally difficult to open, sometimes requiring customers to use scissors or a knife to open. Trauma shears have been demonstrated as particularly effective at opening packaging of this type. This can be frustrating to the point of wrap rage.