Reticulated vitreous carbon (RVC) is a porous carbon sponge. It is a low-cost, lightweight, machinable material that is manufactured easily. RVC has three important advantages compared to thermoacoustic ``stack'' materials that are used currently in prime movers and refrigerators: RVC is impervious to high temperatures; it has an extremely low thermal conductivity; and it has a high specific heat. In addition, there are no ``straight through'' optical paths like those in parallel-plate and conventional pin stacks, so that RVC may inhibit acoustic streaming. Theoretical thermoacoustic models for these RVC stacks do not exist, so the approach is empirical. Measurements are reported of the performance of several RVC stacks with different pore sizes, in a thermoacoustic prime mover and a thermoacoustic refrigerator. Initial results indicate a very good onset temperature and amplitude performance that in some cases exceeds the performance of traditional plastic roll and wire mesh stacks. [Work supported by Office of Naval Research.] [sup a)]Work performed under the auspices of U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.