I've made mine with rice. It works great. It gives off a moist heat when you heat it in the microwave. I put mine in for 2 min. on high. I have a rectangular one about 9x5 that is great for my knee and I have one shaped like a collar for around my neck and shoulders.

Also about the leg cramps when you are in bed. This sounds really silly, but I read it in Hints for Heloise and people wrote back to tell her how great it worked. She said to put a bar of soap under the sheet at about the area where your cramped leg would be. She even suggested tying a thin ribbon around the soap and pinning it to the sheet. Anyway, when you get the cramp, you just put your leg onto that bar of soap and it goes away. I am for trying anything and this, although silly sounding, is a very inexpensive thing to try.