Heat Sealing (a.k.a. RF Sealing, RF welding. Di-Electric Sealing) is the process of joining thermoplastic films using radio frequency energy.  The RF energy is directed through electrodes (dies) shaped to the desired configuration of the finished product.  This makes RF Sealing the most versatile of the plastic sealing methods.  One constraint of this method, however, is that there are limited materials which can be welded with RF.  Acceptable materials are primarily vinyls (PVC), ether and ester-based urethanes (PU), and chlorinated polyethylene (CPE). These materials are often coated or laminated onto substrates for additional strength and versatility.