Clamshell is where the product and the printed card inlay are both encapsulated between two layers of plastic.
The main advantage of these packs is the product inside is clearly visible from the front and back. Depending upon the application and budget the clamshell can simply be hand closed or can be more securely heat sealed or high frequency welded. In high frequency welding, the plastic film is heated when subjected to a high frequency electric field until melting point is reached. This type of blister pack is designed for high value products to make them deliberately difficult to open and therefore eliminating any possibility of tampering with the product inside.