I make mine using a double layer of muslin. Size and shape depend on what I want to use them for. The ones I made for my dh to use on his knees were 9 x 10 inches, and I put 1 lb and 13 oz of rice in them. Make sure the seams are good and tight. I make a removable cover for them. The best way is to make a pillow sham by using fabric that is twice the length plus about 5 inches. I turn the edges over about a 1/4 inch and sew down. The fabric is places with right sides facing, and the extra inches are on the inside of this fold, so that when you turn it out, the right side shows. Sew the seams, flip, and you should have a perfect little pillow sham to fit over the rice pack.