Pellon’s Wrap-N-Zap is a microwave safe product made of 100% natural cotton batting. When used in the microwave, it traps the moisture inside to produce a perfect baked potato or a well steamed ear of corn. If you haven't used Wrap-N-Zap before, you can find a free "Baked Potato Zapper" pattern from Pellon here to try it out.
Note that precautions should be taken when projects are intended for use in a microwave. Use only 100% cotton batting, thread, and non-metallic fabrics to avoid fire hazards.