Dielectric heat sealing is accomplished by sending a high frequency (heating) current through two or more layers of thermoplastic material placed between two sealing electrodes or dies. One die is shaped in the image of the required seal. The other die may have the same shape or may be a flat plate. The dies are usually mounted on a pneumatic or hydraulic press to provide pressure for fusing materials. The high frequency energy produces localized heating of the materials , causing them to soften & melt, thus allowing their molecules to intermingle, where upon the pressure exerted on the material brings about a thorough fusion. The current is then shut off allowing the material a brief cooling period. The resulting seal can be as strong as the original work piece materials.