The actual working of heated pillows depends on the type of pad. In the case of an electric heat pad, the heat is produced by an electrical coil inside the pad. The electrical resistance converts electricity to heat energy. There will be a layer of foam or gel inside the pad to dissipate the heat uniformly across the pad. On the other hand, microwave heat pads do not have a heating coil. Instead, they will use many microwave generators that will, in turn, heat up the filler material inside the pad. Unlike either of these pads, moist heating pads do not have heating coils or microwave generators.