well here goes, I have tried rice bags, bean bags, and corn bags, like the kind you use for corn hole games,
and let me tell you, the rice bags turn into moist heat..which is nice if you need moist heat, but not nice if you are trying to warm up your feet. the bean bags, less than a minute in the microwave, start to smell.. the one bag i can say I like best is my corn bag. Yes it smells a little, but not as bad as the beans.
good luck
katz