A microwave pillow is a heating pad made out of some sort of dry grain or bean filling. In my pillow, I used red lentils because that was what I had in the pantry.
I wanted the pillow to be large enough to tuck both feet under while I'm sitting in a chair, so it needed to be fairly long. Here's what I did:
1) Take a fat quarter of quilter's cotton. Fold in half, right sides together. Stitch around the three open sides, leaving a gap open on one side.
2) Turn the case inside out by pulling the fabric through the gap. The seam allowances should now be on the inside of the case with the right side of the fabric on the outside.
3) Fill the pillow. I used lentils, rice or beans would also work. I made a funnel out out of card stock to make this step easier. My pillow case is half full.
4) Once the pillow is stuffed to your liking, stitch up the gap. Your pillow is ready to zap!
5) Finally, stick the pillow in the microwave. I set mine on a plate to keep it clean. Zap for a minute, shake the pillow a bit to distribute the heat, then heat further in 30 second intervals until it's warm enough. Here's what mine looks like when laid out flat:
When the lentils spread out along the full length of the pillow, it's about an inch thick. It stays warm for over an hour. It's also great to throw under the covers at night to warm up the bed or throwing over your shoulders to soothe a sore neck.