I make these all the time for myself and as gifts! I use flannel fabric, purchased when it is on sale. You can make them any size you want; square, rectangle, u-shaped (to fit around your neck), even 18"-12" and quilted in three or four sections to hold the rice in place.
Use newspaper cut in various shapes to find your desired pattern. Once you decide on how big and what size, cut out the flannel. With flannel pieces right side to right side, sew a 1/4 " seam around all four sides, leaving a 2 inch space or so on one side open. Turn inside out and fill with the cheapest plain rice you can find (Sam's Club sells it in 50 lb bags.) I also add some dried lavender, so that it doesn't smell like baby cereal when cooked. (I use a funnel to get the rice and lavender in)
I fill them about 2/3 full, so that they have some give and can adapt to whatever body part you're using them on. After filling, just sew closed the hole. I store them in plastic zip-lock bags, to keep out the dust/freezer smells and keep in the fragrance.
Microwave heating time depends upon the size -- anywhere from 3-4 minutes to 10 minutes. Each night I heat about 3 -4 large bags and use them to warm up the bed so I don't have to put my cold feet on my husband! (He is very grateful!) ... View related article.
