A novel hybrid compressive mica seal was developed that showed a reduction of leak rate by about 4300 times (compared to simple mica seals) at 800 degreesC. The hybrid compressive mica seal is composed of 2 compliant glass layers and a mica layer. Three commercially available micas were tested in hybrid compressive seals for solid oxide fuel cell applications. The best results were obtained using Muscovite single crystal mica. The normalized leak rate for this seal at 800 degreesC was only 1.55 x 10(-4) sccm/cm at a stress of 100 psi and a pressure gradient of 2 psi. Seals based on the other commercial micas (Muscovite and Phlogopite mica papers), also exhibited superior leak rates (similar to0.011 sccm/cm) compared to simple mica seals without the compliant glass layer (about 6-9 sccm/cm). The microstructure of the mica was examined before and after the 800 degreesC leak tests using scanning electron microscopy. The cause for the substantial reduction of the leak rate was discussed. In addition, the effect of the compressive stresses was also investigated.