What is RF Sealing? How does it work? RF Welding ( Radio Frequency Welding ) machinery usually called RF Heat Sealers are used to bond a variety of plastics. A RF Sealer operates similarly to a standard kitchen microwave oven. When the RF is applied it excites or agitates the polarized molecules in the plastic causing heat. When pressure is applied to the plastic the molecules of the two layers flow together. The resulting bond is usually stronger than the individual layers of material. RF Welders and Sealers usually operate at 27.12MHz.